VLOOKUP / ISNUMBER / SUMIF Stumped, can't get formula to run

I am stumped. I can do a VLOOKUP - been using excel since the Lotus 1-2-3 days. I am usually pretty resourceful with formulas, googled, picked another intermediate users brain and I can't get a formula to work.

I am matching the number in sheet 1, column A to sheet 2 column A and if they match I need to then populate information from sheet 2 column C into sheet 1 column B

Can anyone assist with a formula? I've tried is number, match, sumif...you name it! I can't get anything to run without errors. I feel like a dunce! I'm usually able to get through complicated formulas. Ugh!