Yes MS Excel is a very good tool for drawing graphs and other stuff. You can also use MS word for drawing charts and block diagrams in word files. For drawing chemical structures, you can use ChemDraw or ISIS draw also, if needed.
I would suggest using Visio for drawing diagrams that is much easier and has more options than Excel. If you don't have Visio, use Google Drawing in Google Drive (when you click on ‘Create’ in Google Dive, you see that option). It's pretty similar to Visio and lets you download your drawings as an image or a pdf, tho Google Drawing has less design features.