James, everything you need is here Sir. https://reducerecoil.com/2015/03/difference-between-glock-gen1-glock-gen2-glock-gen3-glock-gen4/

Hi,
The easiest way to determine generation of glock is to look at the grip. Glock Gen 3 and Gen 4 have finger grove. Glock Gen 1, Gen 2, and Gen 5 does not have finger grove. Glock 19 Gen 3, Gen 4, and Gen 5 have rail for mounting light/laser. Glock Gen 4 also have changeable back straps to allow a greater choice of grip thickness for those with smaller or larger hands. I hope this helps.