Fire Spin does damage like a normal attack at first, a special fire type move power 15, and then traps the target, damaging them its base power of 15 at the end of each turn, lasting 2-5 turns. The target will be unable to attack when it is trapped by Fire Spin, but the user of the move can still use other attacks against the target. Something to note would be that if the user switches out before Fire Spin ends, the target will still be unable to attack during that turn. Also, if the target switches out while Fire Spin is still raging on,
Fire Spin will automatically be used against the incoming Pokémon, deducting an additional PP from the move. If at such a time Fire Spin has 0 PP, Fire Spin will still be used against the incoming Pokémon. After that use, the current PP of Fire Spin will roll over to 63, and full PP Ups will be applied to it.
This describes a famous trapping Glitch in Gen 1 where trapping moves can have 63 PP!
Hope you found this helpful!