Enroute Controller providing vectors for an ILS approaches indicated the aircraft in question were high and controller familiarity with and training for these types of operations were minimal.

Narrative

Aircraft X was the first of 2 aircraft requesting vectors to final at ZZZ1. I gave him a descent clearance to 4000 but he did not descend very quickly and was still at 7000 in the general area where I thought they should be down to 4000. He kept getting closer and closer to the outer marker and I was unsure what to do and ended up clearing the aircraft for the approach at 4000 which was the MIA in that area. I was also having trouble hearing his radio and the pilot had made a request that I could not hear or understand. After several requests to repeat; he finally just said 'never mind' and kept heading for the airport. There was also a tanker in trail looking for the same approach and I had a similar problem with the altitude. The aircraft was at 11000 and I requested him to make a 360 in an attempt to lose some altitude and he helped me by descending 600 feet. I eventually cleared him for the approach at the MIA as well. I tried to ask the other controller in the area for assistance but he was busy working his own traffic. I was unsure of what to do with either aircraft because they were so high and I had only vectored to final once before. I have never had any training on vectoring to final at any airport and am not a pilot so when I was told later that you can't clear for the approach if the plane is too high and am supposed to follow a chart buried in ERIDS somewhere; with altitude requirements for certain distances from the airport; I realized I had done just about everything in this scenario wrong. Recommendation; [provide] training on vectoring to final at our airports; especially at airports we don't usually provide that service. Also; it would be nice to have some sort of better training on flying. I don't have an aviation background and don't always know or understand what a plane can or cannot do or why they request certain things. It just adds to the confusion.