Possible Duplicate: How to look up a symbol? Escape character in LaTeX In the itemize environment, how do I use the ampersand symbol & without LaTeX trying to use it as a command?
How do I use '&' literally in LaTeX? - LaTeX Stack Exchange
How does one insert a "" (backslash) into the text of a LaTeX document? And how does one insert a "~" (tilde)? (If you insert ~, it will give you a tilde as an accent over the following letter.) I
How does one insert a backslash or a tilde (~) into LaTeX?
Sometimes the symbol := is used to denote a definition. For example, X:=Y+Z means that X is defined to be Y+Z. When using LaTeX, can I just use $:=$, or do I need to do something special?
LaTeX still supports it for one reason or another, but the "proper" one to use, as defined in the specifications, is [ ... ]. All this just means that they are not promising that $$ will always work. So it is technically possible (though unlikely in the near future), that compatibility with $$ is removed from LaTeX and lots of your documents ...
Why is \ [ ... ] preferable to - TeX - LaTeX Stack Exchange
There is no difference between LaTex and Overleaf. Overleaf uses LaTex. You write LaTex documents in Overleaf. Whenever you have a problem with your document not looking like it should, yo can do a web search for LaTex, and you can apply all information you get regarding LaTex in Overleaf, because thats what Overleaf is.