What is the difference between I will and I should?

I’ll or I will is future simple tense.

We use the Future Simple:

For on-the- spot decisions

We use the Future Simple Tense to talk about decisions made at the moment of speaking. This means that we haven’t thought about the action before and we haven’t planned it.

Example:

(At the shop) I will buy the red T-shits. It fits me better than the blue one

For predictions about the future

We can use the following phrases and words: I think, I believe, I am sure, I am afraid, probably, maybe, perhaps, etc.

Example:

In the future people will live underwater.

I am afraid he won’t pass the exam.

Maybe she will come later tonight.

They will probably call you tomorrow.

For future facts

These are actions and events that we cannot control and they will definitely happen in the future.

Example:

He will be 25 next month.

For promises, threats, warnings, offers, hopes and requests.

Example:

I will call you when I get there. (promise)

I will call the police. (threat)

He will tell the teacher. (warning)

I will help you. (offer)

She hopes she will become a famous singer. (hopes)

Will you give me your pen, please? (request )

You can read more about future simple and do a quiz here.

Should is a modal verb. We use it to give advice.

Example: You should eat more fruit and vegetables.

You can read more about modal verbs and do a quiz here.