AS can be:
- a preposition meaning in the capacity of / in the function of like in the sentence:
She works as a teacher.
- but it is usually a conjunction of manner and goes therefore followed by a verb form, for example:
When in Rome do as Romans do.
- It also appears in comparative structures:
Peter is as tall as a my brother.
- In the group such as it means like:
There are different ways of travelling such as (=like) walking, flying or driving.
Is a preposition and goes therefore followed by a noun. It expresses similarity:
She feels like a rolling stone (=in the same way as)
It was like a dream (=similar to)
Like is a preposition and is therefore followed by pronouns in the object form.
They said they didn't want people like me in that group.
It can also be followed by a verb, in the -ing form
There's nothing like fishing from a boat.
In fact, when we want to ask about the description of something we use:
WHAT IS something LIKE ? which is quite different from
HOW is something /someone ? where we become interested in personal state, etc.