Hi, southwoman!
First of all welcome to Chandoo's website Excel forums. Thank you for your joining us and glad to have you here.
As a starting point I'd recommend you to read the three first green sticky topics at this forums main page. There you'll find general guidelines about how this site and community operates (introducing yourself, posting files, netiquette rules, and so on).
Among them you're prompted to perform searches within this site before posting, because maybe your question had been answered yet.
Feel free to play with different keywords so as to be led thru a wide variety of articles and posts, and if you don't find anything that solves your problem or guides you towards a solution, you'll always be welcome back here. Tell us what you've done, consider uploading a sample file as recommended, and somebody surely will read your post and help you.
And about your question...
If you haven't performed yet the search herein, try going to the topmost right zone of this page (Custom Search), type the keywords used in Tags field when creating the topic or other proper words and press Search button. You'd retrieve many links from this website, maybe you find useful information and even the solution. If not please advise so as people who read it could get back to you as soon as possible.
Conditional formatting just does what it says: format a cell with one or many different formats depending on excluding conditions for its value.
In your case select all cells of required range to be controlled in worksheet "A", go to Start tab, Styles group, Conditional Format icon, New Rule option, Rule Type Use Formula (last option) and enter as formula:
=A1<>B!A1
click on Format, Fill/Background tab, choose your favorite color, Accept.
Just advise if any issue.
Regards!
