The last few days, I've been going to an auto repair shop, in order to learn about the cars because I'm really interested oin that themesubject.

It has been such a great experience,. I don't work directly with the cars too much, but the mechanic explains me what isto me everything we are working with.

Auto rRepair sShop

Usually, titles are written in "title case"

The last few days, I've been going to an auto repair shop, in order to learn about the cars because I'm really interested oin that themeopic.

"theme" has different connotations in English, like "lección" or "diseño" sometimes

"topic" would be more appropriate here

the phrase is "interested in"

commas are used after phrases like "in order to," not usually before them

It has been such a great experience,. I don't work directly with the cars too much, but the mechanic explains to me what is everything is that we are working with.

you could also use a semicolon instead of the period I added

you could also try:

Although/Even though I don't work with the cars too much, the mechanic explains to me what everything is that we are working with.

I'll be going all this week, so I have two more days to keep learning.

"this" is already understood--it might be heard like this in conversations or seen in reading, but the correction sounds more natural

Auto rRepair sShop

All words in a title are generally capitalised.

The last few days, I've been going to an auto repair shop, in order to learn about the cars because I'm really interested oin that themeopic.

(1) The placement of the second comma might be a little awkward. I'd personally remove it.
(2) The phrase is "interested in (something)".
(3) "Theme" is used when referring to things like talks, essays, literature, art, etc. Otherwise "topic" is generally the word to use here.

It has been such a great experience,. I don't work directly with the cars too much, but the mechanic explains to me what is everything we are working with is.

(1) The phrase is "explain to (someone)".
(2) "What is (something)" is used in questions, while "what (something) is" is used in statements. The sentence you wrote is a statement, so the latter is appropriate. In informal contexts like casual conversation, however, both are acceptable here, though the latter is still the grammatical one.
(3) Alternatively: "the mechanic explains to me everything we are working with."

The last few days, I've been going to an auto repair shop, in order to learn about the cars becausecars, as I'm really interested oin that theme.

Really just needed to correct on to in at least. But this seems more natural. It’s a very long sentence ideally you would break it in two.

It has been such a great experience, I don't work directly with the cars too much, but the mechanic explains me what isto me everything we are working with.