Si sé sumar y restar bien, luego me resulta más fácil hacer cualquier cálculo.

Because sé here is the 1st person singular of saber: I know.

The accent is there to distinguish it from se, which is a very common pronoun in Spanish.

• sé = I know
• se = himself / herself / itself / themselves, or part of other verb constructions

So in Si sé sumar..., sé means if I know how to add...

They are two different words:

• si without an accent = if
• sí with an accent = yes, or sometimes himself/herself after a preposition

In this sentence, si introduces a condition, so it must be si = if.

• Si sé sumar... = If I know how to add...
• Sí, sé sumar = Yes, I know how to add

Because this is a real or general condition. Spanish normally uses:

• si + present indicative, then
• a present, future, imperative, or similar result clause

So:

• Si sé sumar y restar bien, luego me resulta más fácil...

This means something like a general truth: if I know how to add and subtract well, then calculations become easier for me.

You would use the subjunctive in a different kind of hypothetical structure, for example:

• Si supiera sumar y restar bien, me resultaría más fácil...
• If I knew how to add and subtract well, it would be easier for me...

Because Spanish often uses the infinitive to talk about an action in a general sense.

Here, sumar y restar means adding and subtracting or to add and subtract in a general skill-based sense.

This is very common in Spanish:

• Leer es importante = Reading is important
• Fumar es malo = Smoking is bad
• Sé cocinar = I know how to cook

So sé sumar y restar means I know how to add and subtract.

It means I know how to add and subtract.

In Spanish, after saber, you can use an infinitive directly to mean to know how to do something.

• Sé nadar = I know how to swim
• Sabes conducir = You know how to drive
• Sé sumar y restar = I know how to add and subtract

So saber + infinitive is a very useful pattern.

Bien means well, and it modifies sumar y restar.

So:

• sumar y restar bien = to add and subtract well

It tells you the person is not just able to do those operations, but does them correctly or skillfully.

Its position is natural after the verbs:

• sé sumar y restar bien

You could also say something more explicit like:

• sé sumar bien y restar bien

But that sounds more repetitive.

Here luego means something like then, after that, or as a result.

It connects the first idea with the consequence:

• If I know how to add and subtract well, then doing any calculation is easier for me

In this sentence, luego does not mean immediately. It simply marks the next logical step.

Also, in Spanish from Spain, luego is very common in everyday language, though depending on context it can mean:

• then
• later
• afterwards

Here the best sense is then / as a result.

Because resultar is being used to express how something is for someone or turns out for someone.

• Me resulta más fácil = It is easier for me / I find it easier

The me means to me / for me.

So the structure is roughly:

• hacer cualquier cálculo me resulta más fácil
• doing any calculation is easier for me

Using resultar makes it sound a bit more natural and personal than a plain es más fácil in this context.

The subject is the whole infinitive phrase:

hacer cualquier cálculo

That entire phrase functions like doing any calculation in English.

So the sentence structure is basically:

• hacer cualquier cálculo = subject
• me = indirect object, meaning to me
• resulta = verb
• más fácil = complement

Literally, it is close to:

• Doing any calculation turns out easier to me

Because the subject is treated as a single idea, the verb is singular:

• resulta, not resultan

Yes. That would also be correct:

• Si sé sumar y restar bien, luego es más fácil para mí hacer cualquier cálculo

But it is a bit less elegant and slightly less natural than me resulta más fácil.

Common options are:

• me resulta más fácil
• es más fácil para mí
• me cuesta menos

All are possible, but me resulta más fácil is a very natural choice here.

Because cualquier is the shortened form of cualquiera used before a singular noun.

• cualquier cálculo = any calculation
• cualquiera = any one, when it stands alone

Examples:

• cualquier libro = any book
• cualquiera sirve = any one will do

So in this sentence, since it comes directly before cálculo, Spanish uses cualquier.

Because cualquier normally goes with a singular countable noun.

So:

• cualquier cálculo = any calculation
• cualquier problema = any problem
• cualquier libro = any book

Even though English sometimes makes learners think of a plural idea, Spanish uses the singular here.

If you wanted a plural idea, you would usually phrase it differently, for example:

• todo tipo de cálculos
• cálculos de cualquier tipo

But cualquier cálculo is perfectly natural.

Because hacer un cálculo or hacer cálculos is a normal Spanish collocation.

Just as English says do a calculation, Spanish often says hacer un cálculo.

So:

• hacer cualquier cálculo = to do any calculation

Other verbs are possible in some contexts, such as:

• realizar un cálculo = more formal
• resolver un cálculo = less neutral, depending on context

But hacer is the most everyday and natural option.

In standard writing, yes, it is normal and recommended to put a comma after an initial si clause.

So this is the usual punctuation:

• Si sé sumar y restar bien, luego me resulta más fácil hacer cualquier cálculo.

That comma helps separate the condition from the main clause.

If the order were reversed, you normally would not use a comma:

• Luego me resulta más fácil hacer cualquier cálculo si sé sumar y restar bien.

Yes. The sentence still works perfectly without it:

• Si sé sumar y restar bien, me resulta más fácil hacer cualquier cálculo.

Adding luego just makes the logical sequence clearer: first one thing, then the consequence.

So:

• without luego = more direct
• with luego = slightly more explicit: then / as a result

Both are natural.