VBA to search and when found to insert in a column a value

Hello! I need urgent help with a task from my working place. I have a list with data to modify in other bigger list, using a stamp. I need "something" to find data from a source table in other bigger table, and when data is found, in a certain column to insert a value. More exactly, a have two sheets and in the second sheet is data to find in the mail table situated in sheet 1. When the data is found in sheet1, where the main table is, a stamp must be inserted.
Thanks a lot!