IF checks a condition and returns one of two results:
=IF(logical_test, value_if_true, value_if_false)
The test compares values with =, <> (not equal), >, <, >= or <=. For example =IF(B2>=70,"Pass","Fail") shows Pass when B2 is 70 or more.
Text results go in double quotes. Numbers don't: =IF(B2>=50000,B2*5%,0) returns a number you can add up later. Two quotes with nothing between them, "", show an empty-looking cell.
Watch the edge of the test. >70 and >=70 give different answers for exactly 70, so decide what should happen at the boundary before you write it.
When you need IF on every row, write it once in the first row and copy it down with the fill handle. The references move with each row.