Ek vergeet soms my handskoene in die motor, maar nooit my serp nie.

Vergeet is in the simple present. In this sentence it describes something that happens from time to time, so it has a habitual meaning: I sometimes forget...

It is also worth noticing that Afrikaans verbs usually do not change much for different subjects. So you get ek vergeet, jy vergeet, hy vergeet, ons vergeet, and so on.

Soms is an adverb of frequency, meaning sometimes. In a neutral Afrikaans main clause, adverbs like this often come after the finite verb and before the object:

Ek vergeet soms my handskoene...

That said, the word can move for emphasis. For example:

Soms vergeet ek my handskoene in die motor...

That is also natural, but it shifts the focus slightly.

Handskoene means gloves. The singular is handskoen.

It is a compound word:

• hand = hand
• skoen = shoe

So handskoen is literally something like hand-shoe. The plural is handskoene.

Because my is already a possessive determiner, like my in English. In Afrikaans, a possessive usually replaces the article.

So you say:

• my handskoene
• my serp

not:

• die my handskoene
• die my serp

Yes. Motor can mean car in ordinary Afrikaans.

You can also say kar, which is very common and a bit more informal. So both of these are natural:

• in die motor
• in die kar

The sentence would still sound normal with kar.

Maar means but and is a coordinating conjunction. Like English but, it links two main-clause ideas.

It does not push the verb to the end. In a full version, the second part would be:

..., maar ek vergeet nooit my serp nie.

So maar behaves differently from subordinating conjunctions such as omdat.

This is normal ellipsis, meaning repeated words are left out because they are understood from context.

The full version would be:

Ek vergeet soms my handskoene in die motor, maar ek vergeet nooit my serp nie.

Since ek vergeet is already clear, Afrikaans can shorten it to:

maar nooit my serp nie

English does the same thing in sentences like I sometimes forget my gloves, but never my scarf.

In standard Afrikaans, nooit normally goes together with a clause-final nie.

So the normal pattern is:

Ek vergeet nooit my serp nie.

Even though nooit already carries the negative meaning, the final nie is still part of the standard Afrikaans negative construction. That is why the shortened second half ends with nie.

In a neutral sentence, an adverb like nooit usually comes before the direct object:

Ek vergeet nooit my serp nie.

That is the most natural word order here. If you move nooit, the sentence may still be possible in some contexts, but the emphasis changes and it can sound less neutral.

It literally means in the car. Here it most naturally suggests that the gloves are left behind there or forgotten there.

So the idea is not just that the speaker is inside the car when forgetting them, but that the gloves end up being forgotten in the car.