Check the components you have first, it is most likely they are OK. FIRST remove the sender unit from the tank, and be sure to fully cover the hole in the tank were the sender came out to prevent anything, including sparks from the electrics, sending the car up in flames.
Disconnect the wires from the sender, and with the ignition on fully earth the lead to the gauge to the chassis, the gauge should then immediately go to a full tank reading. Turn off the electrics at the ignition switch.
If OK, next reconnect the wires to the sender, and with the ignition feed back on raise and lower the float level and check that the gauge reads a position equal to the float level, fully down should be empty, fully up should be full, halfway should be - got it ? Check that the float when in the tank is showing correct reading, bending the wire that holds the float to achieve the reading on the gauge,