can i swap my 8 speed shiamno claris cassette to a shiamno 10 speed Tiagra ?

yes if you swap shifters.

And the rear mech. The pull ratio is different. The shifter has to match rear mech, so the amount of cable pulled by the shifter moves the mech the correct distance.

Both have to be 10 speed, but not the same model, but the same manufacturer. Shimano with Shimano, SRAM with SRAM, etc.

so if i buy a rear mech and new shifter im ok to go?

if i buy rear mech leavers

and you will need a 10 speed chain. 8 speed chains are too fat.