Wont shift out of first gear

Either the fluid is very low, or fluid is not being pumped through the transmission.

Start out first by checking the transmission fluid while the truck is at operating temperature. If the transmission oil is low, check under the truck for any signs of leaks. If it's leaking from the transmission pan, transmission lines, or at the radiator... it's usually an easy fix.

If your transmission fluid is ok or low without signs of leaks, have it towed to a transmission shop. Don't drive it or you may risk more damage.