You can use either a dive bottle with a paintball fill station, or a paintball / PCP air rifle compressor.
The fill valve is on the tanks primary regulator (shown here)
You cannot fill your tank on a 'workshop' compressor. Your compressor must be capable of producing 3000PSI+
The steps required for filling your tank vary based on the equipment used, always consult the manufacturers instructions, or a marshal when filling your tank for the first time.