Depending on your native language, some of these grammar issues could be a little tricky
with the period.
Never put a space before it, always put a space after.
So at the end of a sentence, last letter, period then a space.
If you're listing things, number, period then a space.
Now, it used to be that two spaces after a period was correct, now we just use one.
Comma, never put a space before a comma, always put a space after just like the period.