In a reversal type clue you need to find a word that when reversed (i.e. read backwards) will produce another word.

Here is a typical reversal-type clue:

Extracted backward jeans (5)

These clues generally consist of three parts:

1. The definition. This is the solution you are looking for, Jeans in the case above.
2. A reversal "indicator" - This is a word (or words) that signal to the solver that the clue is in fact a reversal clue. Because reversals are all about reading things the other way, reversal indicators tend to be words that signify that, like backwards above.
3. A clue to the word(s) that when read backwards result in the definition. In this case Extracted.

In this case:

• Extracted = Mined.
• Jeans = Denim.

Extracted, when read backwards, becomes Denim.

There aren't that many words that read backwards into other words. So you tend to find reversal-type clues combined with other clues into a bigger clue.

Now try this clue:

If you are stumped, give it to the machine!