Cornell SPS holds tutorials on Mathematica, LaTEX, or Python every year. We've also listed below some websites which might be useful for learning to use them.
For beginners, Overleaf is an online editor for writing documents in LaTEX and is straightforward to use. Overleaf provides a useful guide to LaTEX: https://www.overleaf.com/learn/latex/Learn_LaTeX_in_30_minutes
If you don't know how to write a symbol in LaTEX, Detexify can save your time: https://detexify.kirelabs.org/classify.html
An interesting website: Learn X in Y minutes. If you want to learn Python real quick, just search for Learn Python in Y minutes.