XLOOKUP(search_key, lookup_range, result_range, missing_value, match_mode, search_mode) finds search_key in one column and returns the matching cell from another. You point at the two columns separately, so there's no column number to count, and the result column can sit to the left of the lookup column.
It looks for an exact match unless you say otherwise, so you rarely need the last two arguments. The fourth argument, missing_value, is what to show when nothing matches, which saves wrapping the formula in IFNA.
result_range can be several columns wide. Then XLOOKUP returns the whole matching row of those columns, and the result spills to the right.
For bands and tiers, set match_mode to -1: an exact match, or else the next smaller value. Skip the arguments you don't need with an empty comma: XLOOKUP(B2, A2:A6, C2:C6, , -1).