that allow me to draw figures (shapes) or graphs and to label them.
I don't know of any websites, however I can recommend some free software for Windows that I have used for simple drawings. Paint.Net is a good one. I have used it for drawings and figures for my classes. The learning curve is very shallow.
Gimp comes highly recommended, but I don't know if there is a windows version (never used it)
Graphs, well, I use excel on my desktop and openoffice.org on my laptop. I have done basic graphs with both of those.
Hope this helps.
Your request in is in a math discussion forum and not very specific with regard to the requirements, so ... tikz. A LaTeX package to make wonderful graphics.
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