The previous answers describe how to use the first column of each index. (in the where clause).
I think it's also important to point out that the second column is useful because it potentially increases performance of queries that involve the second column.
The following query will be completed with JUST an index seek on IDX_1, saving valuable lookups to the base table (since val2 is already part of the index).
SELECT val2 from IndexTables where val1 = @someVal1
Likewise, the reversed index will optimize this query:
SELECT val1 from IndexTables where val2 = @someVal2
However, only one (it doesn't matter which) of the two indexes is need to optimize the following query:
SELECT val1, val2 from IndexTables where val1 = @someVal1 and val2 = @someVal2
This shows that, depending on the queries your table receives, there may be a legitimate reason to have both indexes.