Krang, Shredder, Bebop and Rocksteady use remote-controlls to pilot the minimizer from a control room inside the Technodrome. Even Bebop and Rocksteady are able to do that.
The minimizer is capable of shrinking anything it fires its rays on. Its purpose is to reduce resistance by shrinking military bases. It then fires a tractor beam at the shrunken object, pulling it inside a hold in the minimizer. Th minimizer is also capable of firing destructive energy bursts. It fired at April O'Neil when she was following it in the news van.
The turtles hijacked the minimizer by jumping onto it, and used it to shrink the Technodrome. The minimizer crashed and was never recovered by Krang. However, since Krang designed the minimizer, he could esally restore the shrunken Technodrome.
The design of the Minimizer appears to be inspired by the Martian war machines depicted in the 1953 film The War of the Worlds. It's green-colored energy bursts further the connection.