Match partial text string in one sheet to another text string in another sheet

Hi All,
I have two different sheets. In one sheet, I have last names. In the other sheet, I have a column that has cells that contain the person's last name and also additional text.
I am looking to create a new column that will
1. look at the other sheet's column
2. see if the last name appears in the column of cells
3. if it does, copy that cell into the new column
4. if it does not, return an "x"

I can't seem to find a formula that will allow me to find "some text" within another sheet's cell.
Please help!

Thank you!