Just need a correction if these sentences are wrong

Hello everyone!

Could you please correct these sentences? If they are correct, let me know that with your comment. Thank you very much!

I have no phone now, I have left it at home. It is at home.

At the playground there are three different slides:
Do you want to slide?
Which slide do you want to slide down?

Do you want me to slide (together) with you?

Do you want me to sit down next to you? (This is a question to a baby, just for learning English; the baby is sitting on the bench and calling me to sit next to her)

Don't play with my keys. These/They are not  toys.

Climb the bench and sit down next to me (this is aimed to a baby too; the baby is short and needs to climb the bench before she can sit on it)

Let's go (to) see the fish!
Let's go to the pond to see the fish!

When playing with a ball. There is wind that moves the ball away (some other place):
The ball rolled away. Where is the ball?

Thank you for your attention!

Why I joined to italki?

Hello everyone! I'm Gabriela, Brazilian and I'm doing my master on health/medical area. I've joined to italki recently and here are some reasons why:

- I wanna improve my pronunciation and vocabulary:

Recently I've traveled abroad for work and I met all "these" (I think you shouldn't specify them) amazing people, a lot of them are native English speakers. But I was so afraid of not being able to communicate well enough with them! Fortunately I did, but I still struggle with it  a bit. So that's one reason why I would like a language exchange and a language partner: I could practice and improve my English and contribute with someone who are also learning with Brazilian Portuguese, which is kinda cool! I will travel again soon, so that's another reason why.
I think I have a limited English vocabulary, specially informal English, and speaking with a native English speaker might help me to expand my vocabulary, learning new words and how to use them.

- I wanna improve my writing:
Sometimes I have to write in English for work: it might be an essay, or an abstract for a Congress, etc, and I struggle with that. I also have the hardest time texting my friends in English. So I started to study by myself, with English grammar books and so on, and I hope I can improve that here on italki.

I guess that's it for my first entry. I might write here more often!
Thanks!
Until next time!

Is German a difficult language to listen to?

I started learning German 3 months ago and I thought I had learned a lot. Until I heard  a conversation today in German and I didn't understand anything. Is German a difficult language to listen to? Maybe I just need more practice, at least I like the way it sounds...

Hello there, how is it going?

About your grammar, it's good. However you made few simple mistakes like:

*Names of languages in English are always begun  with uppercase letters.

*The verbal tense defines your position in the time, so at the first line, the auxiliary verb "Have" has to be put on past tense (had) because you thought about something before you realize something.

*The structures of the sentences are build in a correct sequence, first the noun which realizes the action, after the verb (the act) and then the time where it was/is done.

*And finally, when you do the act of "listen", you always listen TO something or someone. In this case. German is the thing you are/were listening to.