5-a: Would you like something to drink ?
b: I will have a cup of tea, please
6- I (belive) it when i (see) it .
I will believe it when I see it
7- When you (meet )them? I (meet)them at 8.30.
When you met them? I will meet them at 8.30. past tense - incorrect.
8- you ( understand ) when you ( be ) older .
you will understand when you were older. past tense - incorrect.
The rest of your sentences are correct.
Punctuation - punctuation marks are put immediately after the word, with a space following the mark. Like this.
Capitalisation - First words in sentences and the personal pronoun "I" are always capitalized.