Conditional Formatting from a separate range?

I am guessing this is simple, but I cannot seem to find a good example when trying to search.

See attached example.

Picture two columns. One of Blanks. One of numbers or values. I want say all the values in the second column to be grayed out as their actual value is added in the first column.

I think conditional formatting does this but I'm having a hard time achieving this.

Any help is greatly appreciated.

Thanks,
Matt