Calculate sum for selected entries in column c plus selected entries in column d.

Extreme novice here and my quick scan of threads did not answer my issue. Apologies if already posted, I just didn't find it.

I have a spreadsheet where I enter my income from contract A (in column B) and income from another contract (in column C). I want to total all of my income for that particular month in a different column so that I can visualize the total income for a particular month. I want to do this for every month. I'm spending a lot of time going nowhere and getting loads of errors in my formulas. Suggestions?

TIA

Welcome to the forum.

It would helps if you attached a sample Excel workbook, and you can do this by following the guidelines in the yellow banner at the top of the screen.

Pete