Present Simple
The present simple is used to talk about facts or general truths:
The sun heats the atmosphere.
The heart pumps blood through the body

It also talks about habits for example, always, usually, often, sometimes, never:
We usually play soccer.
You always work.

It's also used to talk about schedules or programs:
The train leaves in an hour.

Another useful rule to consider when using the present simple is the form of the verb with the 3rd person singular:

When the verb ends in s, or a similar sound such as sh, ch or x add es:

Watch > watches

Dash > dashes

When the verb ends in o, we also add an es:

Go > goes

Do > does

When the verb ends in y, and it is preceded by a consonant, we have to change the y to i, and then add es:

Fly > flies

Study > studies

Present Continuous
The present continuous can be used to express different things, and in different circumstances:

To refer to actions that are developing at the time of speaking.

Go away, I am reading a book! (right now)

We also use the present continuous to describe things that happen around the time we are talking.

She is studying English. (not just now)

We can use the present continuous to refer to actions that have taken place with some frequency.

You are always working. (it happens frequently)

When we speak of a future action that we know will be done. In this case we must mention the time in which we will complete the action.

I am going to Madrid next week.