Conjunctions

Conjunctions are words that join two ideas together. These are things like:

and

but

or

Correctly done, that would sound like:

I smiled at the girl next door and she smiled back.

Of course, it must be a complete idea unless it is in a series. Perhaps your language has some different rules. Observing how it sounds and how it's written will let you have a better guide for them. Otherwise, it would read:

I smiled and back.

When used in a series, and usually completes it out. It would look a lot like this:

I see cats, hats, and bats.

Improper usage would look something like:

I see cats and hats, bats.

Conjunctions can also be used to connect two words together just like this.

I see cats and hats.

Don't forget to practice your writing time again. You're getting better every day. I suggest doing the same thing consistently and improving over time. Then once you're sure you have it down, you can go somewhere else and try again. Or perhaps you could build from what you already know.