New above ground pool. filter/pump start up problem - please HELP

hey,
just bought and had put up a 18x33x52 above ground pool (15 000 gal)

bought Pro Above Ground Swimming Pool Pump System 4500GPH 19" Sand Filter w/ 1.0HP

and a pool frog system. All is hooked up, NO cartridge in pool frog yet.
Pool just filled up and I

Tried the initial start up filter backwash ...... after priming pump. initially the water comes gushing out but 2 sec later NO pressure :( Pressure gauge doesn't move either.
Priming pump I couldn't really find the relieve valve. Instructions are for the birds.

do I need to wait until there is more water in the filter ?

I'm a t a loss now and afraid I burn pump if I keep trying ?

thanks