Learn German: Er lässt das Auto hier. - He is leaving the car here.

Lassen is a strong verb. In the present tense, many strong verbs with an a in their stem change that a to an ä (a-Umlaut). This vowel change only happens for the du (you) and er/sie/es (he/she/it) forms. Since the subject here is er, lassen becomes lässt.

The stem of lassen ends in an 'ss'. How do the verb endings work here?

For the er (he) form, we add a -t to the stem, which gives us lässt. Interestingly, the du (you, singular informal) form is also lässt. When a verb stem ends in an s, ss, ß, or z, we don't add an extra s to the usual -st ending for du. Both forms end up looking exactly the same!

I thought lassen meant 'to let'. Why is it translated as 'leaving' here?

Lassen is a very useful verb with a few different meanings! While it often translates to 'to let' or 'to allow' (like 'let it go'), it is also the standard word for 'to leave' an object somewhere. Just like in English, you can 'leave the car here' (das Auto hier lassen).

Is das Auto the subject of this sentence?