"lassen" is a verb that can serve different functions and have different meanings.

"lassen" as a main verb
As a main verb, "lassen" can often be used on its own and usually means to stop or to have stopped doing something. It can also be defined as "to let be" or "to leave be".

Example:
Helmut: Alle mal herhören! Anna hat heute Geburtstag!
Anna: Helmut, lass es!
(= Anna will nicht, dass alle erfahren, dass ihr Geburtstag ist. Helmut soll aufhören, sie zu ärgern.)

"lassen" as a helping verb
As a helping verb, "lassen" is used in conjunction with another verb in the infinitive. This is similar to constructions with modal verbs. In this case, "lassen" can have different meanings, such as

1. lassen = to let, to allow something

Example:
Helmut: Anna, bitte lass mich gehen!
(= Helmut möchte, dass Anna ihm erlaubt zu gehen.)

2. lassen = to cause, bring about something, to get something to happen
In this sense, "lassen" means to cause something to happen or to get something done.

Example:
Anna: Wenn ich aus der Zeitschleife rauskomme, dann lasse ich Helmut verhaften.
(= Anna wird dafür sorgen, dass Helmut verhaftet wird.)

3. The imperative of "lassen" as a command for the 1st person plural
In German, there is no imperative form for "wir". To construct it you use either the formal imperative together with the personal pronoun or "lassen" as a helping verb. For example, you'd say "Lass uns etwas tun!" when referring to yourself and another person, and "Lasst uns etwas tun!" when you mean a group of people.

4. sich … lassen = man kann
The phrase "sich ... lassen" is similar in meaning to the modal verb "können". It indicates a possibility and can be used as a substitute for a passive sentence with "können". Whatever it is that can be done is described by the verb in the infinitive.