Here are the characters which are used in LaTeX as they are. Which means that the LaTeX codes for these characters are the same as they are written in Text.
For example, to write a+b=0, one need to write $latex a+b $.
Other characters which can be used as-is in LaTeX are:
Symbols like: +, -, /, %, ?, !, *,~,#,|, =, ¡ ;
Small Letters: a,b,c,…z;
Capital Letters:
To test anything, type $latex Your LaTeX code$.