Explanation
This is a very simple application of the VLOOKUP function set for "exact match":
- lookup value comes from C5
- table array is the named range "points_table" (F5:G7)
- column index is 2, since points are in column G
- range lookup is 0 (FALSE) to force exact match
Because we are using VLOOKUP in exact match mode, the points table does not need to be sorted in any particular way.
VLOOKUP is a nice solution in this case if you want to display the points table as a "key" for reference on the worksheet. If you don't need to do this, see the nested IF version below.
Nested IF version
To calculate win/loss/tie points with the IF function, you can use a simple nested IF:
=IF(C5="Win",3,IF(C5="Loss",0,IF(C5="Tie",1)))
See this article for a detailed overview of nested IF formulas.