How to Assign Value to a String & Replace String With Assigned Value?

I have two sheets in my workbook
Sheet 1:
Column 1 | Column 2
abc | 2
xyz | 3
dki | 4

and many rows following…
How do I assign the variables in column 1 with the values in column 2 for the entire columns?

Sheet 2:
| Column 1 |
| cde |
| cfe |
| cdx |

and many rows following…

How do I automatically replace the strings in column 1 (sheet 2) with the assigned value (in sheet 1) if the string matches with the variables set in sheet 1, and if the string doesn’t match any variables in sheet 1, 0 will replace the string.

Or is there an easier way to achieve this?

Thanks in advance!!