Working from the inside out, MATCH is used to locate the position of the first match in the range B5:D5. The lookup_value is based on the value in B5 joined with an asterisk (*) as a wildcard, and match_type is set to zero to force an exact match:
E5 contains the string "calc" so, after concatenation, the MATCH function looks like this:
and returns 3 inside index as "row_num":
Although the range B5:D5 is horizontal and contains just one row, INDEX correctly retrieves the 3rd item in the range: "calc 1500".