Verbs

The verb has a central role in the clause and it is rare to omit it from a clause. 

The fish (subject) eats (verb) fish food (object) by the handful (adverbial).

We can remove the adverbial: The fish eats fish food.

The object: The fish eats by the handful.

The subject, in casual style: Eats fish food by the handful. (Pointing at the tank).

But we cannot omit the verb: The fish fish food by the handful. 

However, there are such things as 'verbless' clauses, which I will look at later on. 

Verb Element

Only one verb element is allowed per clause. Sometimes that will just be one verb:

John (subject) went (verb) home (adverbial).

Or multiple verbs working together to form one meaning:

John (subject) has gone (verb) home (adverbial).

Although 'has gone' is two verbs, they work together to express one thing, so they count as one verb element. 

Intransitive Verbs

These are verbs that can be written without an object:

The builder's going. 

Some common intransitive verbs are:

appear

die

digress

fall

go

happen 

lie

matter

rise

wait

Transitive Verbs

Verbs which require an object are traditionally known as transitive verbs. Enjoying is an example:

The builder's enjoying his lunch. 

Some common transitive verbs are:

bring

carry

desire

find

get

keep

like

make

need

use

Some verbs can be used intransitively or transitively. For example:

She's expecting a reply. She's expecting. 

He worked wonders. He worked.

As you can see from the example, what often happens is that the verb changes meaning when used in these different ways.