PGT is Trained Post Graduate that means a persons who has done post graduation and also possess a B.Ed degree from any valid university. For B.Ed u can approach IGNOU for 2 year correspondence course while PTET is for regular candidates of one year. For regular course you will have to give an entrance . the colleges are alloted on teh basis of merit.
PGT is the essential qualification if u want to opt for a career in teaching . all CBSE schools require either TGT or PGT.