Je confonds souvent ces deux mots.

Because confondre is the verb meaning “to confuse / to mix up”, and its present-tense forms are:

• je confonds
• tu confonds
• il / elle / on confond
• nous confondons
• vous confondez
• ils / elles confondent

Confus exists in French, but it’s usually an adjective meaning “confused / unclear”, not a verb form.
So you say je confonds ces deux mots (“I confuse these two words”), not je confus.

In this sentence, confondre means “to mix up”, i.e. to mistake one thing for another:

• Je confonds souvent ces deux mots.
  → I often mix these two words up.

Other common uses:

• confondre quelqu’un avec quelqu’un d’autre
  → to mistake someone for someone else
• La mer se confond avec le ciel.
  → The sea merges / blends with the sky.

So in vocabulary contexts, confondre = “mix up,” not “make someone feel confused.”
For “make someone feel confused,” you’d more often use something like déconcerter, embrouiller, or rendre confus.

In French, short adverbs of frequency like souvent (often), toujours (always), rarement (rarely) usually go after the conjugated verb:

• Je confonds souvent ces deux mots.
• Je mange souvent ici. (I often eat here.)

So je souvent confonds is incorrect; the standard position is verb + souvent.
You can move souvent to the beginning for emphasis: Souvent, je confonds ces deux mots, but then it’s separated by a comma and sounds more “topic–comment”/stylistic.

Souvent normally corresponds to “often”.
If you want to intensify it (“very often”), you’d say:

• très souvent
• bien souvent (quite often / often enough)

So Je confonds souvent ces deux mots is simply “I often mix up these two words,” not necessarily “I constantly / all the time mix them up.”

Ces is a demonstrative adjective meaning “these” or “those” in front of a plural noun.
The structure is:

• ces = these/those
• deux = two
• mots = words

You don’t use les (the) at the same time as ces; it’s one or the other:

• ces deux mots = these two words
• les deux mots = the two words

So ces deux mots specifically points to words that are “near” in context (the ones we’re talking about right now, maybe on the page in front of us).

French has a fixed word order inside the noun phrase:

[determiner] + [number] + [noun] (+ adjectives, etc.)

So you get:

• ces deux mots (these two words)
• les trois filles (the three girls)
• mes deux meilleurs amis (my two best friends)

Reversing ces and deux (deux ces mots) is ungrammatical.

French doesn’t need an extra preposition here.
With confondre, you often just say confondre X et Y or confondre ces deux X:

• Je confonds souvent ces deux mots.
• Je confonds “jour” et “journée”.

If you want to use entre (“between”), you’d normally change the verb, for example:

• Je n’arrive pas à faire la différence entre ces deux mots.
  → I can’t tell the difference between these two words.

Approximate pronunciation (in IPA):
/ʒə kɔ̃.fɔ̃ su.vɑ̃ se dø mo/

Details:

• Je → /ʒə/
• confonds → /kɔ̃.fɔ̃/ (final -ds is silent)
• souvent → /su.vɑ̃/ (final -t is silent)
• ces → /se/
• deux → /dø/
• mots → /mo/ (final -ts is silent)

There is usually a liaison between deux and mots, so you hear something like /dø‿mo/ as one unit.

Yes. You can replace ces deux mots with les (them), a direct object pronoun:

• Je confonds souvent ces deux mots.
• Je les confonds souvent. → I often mix them up.

Notice the pronoun les goes before the verb confonds.
In spoken French, if it’s very clear from context, people might just say Je les confonds souvent without repeating the noun.

You wrap ne … pas around the verb (and any object pronoun):

• Je ne confonds pas souvent ces deux mots.
  → I don’t often mix up these two words.

With a pronoun:

• Je ne les confonds pas souvent.

In casual speech, people often drop the ne:
Je confonds pas souvent ces deux mots, but in writing and careful speech you should keep ne.