Αν γράψω λάθος λέξη, τη διαγράφω αμέσως και αρχίζω ξανά από την αρχή.

After αν in this kind of condition, Greek normally uses the subjunctive form. Here, γράψω is the aorist subjunctive of γράφω.

So:

• αν γράψω = if I write / if I happen to write

It does not mean past time here. It expresses a possible action in the condition.

Because αν itself introduces this kind of subjunctive clause. In other words, Greek says:

• αν γράψω = if I write

not:

• αν να γράψω

So γράψω is still a subjunctive-type form, but after αν, να is not used.

This sentence describes a general habit or what I do whenever this happens.

So the pattern is:

• αν + subjunctive for the condition
• present tense for the repeated result

That is why Greek says:

• Αν γράψω... τη διαγράφω... και αρχίζω...

Meaning roughly:

• If I write a wrong word, I delete it immediately and start again

If you wanted a single future situation instead, Greek would more likely use θα in the second part, for example:

• Αν γράψω λάθος λέξη, θα τη διαγράψω...

Here λάθος means wrong or mistaken.

Literally, λάθος is very often used as:

• a noun: mistake
• an adverb: wrongly
• an adjective-like word before a noun: wrong

So:

• λάθος λέξη = wrong word

A more formal or fully adjective-based version would be:

• λανθασμένη λέξη

But λάθος λέξη is very natural in everyday Greek.

Because λάθος is commonly used as an indeclinable word in this kind of expression. It does not change for gender, number, or case here.

So Greek can say:

• λάθος λέξη
• λάθος απάντηση
• λάθος αριθμός

without changing λάθος.

Greek often leaves out the indefinite article where English uses a or an.

So:

• γράφω λάθος λέξη
  can naturally mean
• I write a wrong word

You could say:

• μια λάθος λέξη

but it is not necessary here. Omitting μια sounds perfectly natural.

τη means it here.

It refers back to λέξη (word), which is a feminine singular noun in Greek. Because the noun is feminine singular, the object pronoun must also be feminine singular:

• λέξη → τη

So:

• τη διαγράφω = I delete it

A small extra detail: the fuller form is την, but before many consonants Greek often uses τη.

In Modern Greek, weak object pronouns like με, σε, τον, τη, το usually come before a finite verb.

So Greek says:

• τη διαγράφω

not:

• διαγράφω τη

This is normal Greek word order for clitic pronouns.
One major exception is the imperative, where the pronoun usually comes after:

• διάγραψέ τη = delete it

αμέσως means immediately, right away, or at once.

In this sentence:

• τη διαγράφω αμέσως = I delete it immediately

Its position is fairly flexible. Greek could also say:

• αμέσως τη διαγράφω

but the version in your sentence is very natural and neutral.

They are related, but not identical.

• ξανά = again
• από την αρχή = from the beginning

So:

• αρχίζω ξανά = I start again
• αρχίζω ξανά από την αρχή = I start again from the beginning

Using both is natural because it makes the meaning more specific: I do not just continue; I restart from the start.

They mean different things:

• από την αρχή = from the beginning, from scratch
• στην αρχή = at the beginning, at first

So in this sentence, only από την αρχή fits:

• αρχίζω ξανά από την αρχή = I start again from the beginning

If you said στην αρχή, the meaning would change.

Because the first part is the if-clause:

• Αν γράψω λάθος λέξη

and the second part is the main clause:

• τη διαγράφω αμέσως και αρχίζω ξανά από την αρχή

In Greek, when the αν clause comes first, it is very normal to separate it with a comma.

So the punctuation helps show the structure:

• If X, then Y.