highlighting cells based on dropdown selection

Hello everyone,

I'm kinda new to Excel (beginner/Intermediate level), and having been recently promoted, my new job involves working with spreadsheets. I have the following two questions, which I hope some of you lovely people here can help me with:

1. I have created a drop down list, so what I would like to do is when an option is selected from the list, a range is in the same worksheet is highlighted in colour and the title of that range (text) is replaced with another text? I hope I'm explaining this well.

2. When two cells in the same worksheet but different tabs have the same value/number, how can I get Excel to create a pop up message?

Any assistance will be very much appreciated. Thank you in advance.