What was luke doing between star wars 5 and 6?

I watched episode 6 and it didn't make sense to me. I assumed that
luke went back to yoda to finish is training. But after he rescued Han
and leia he goes back and said "I'm ready to finish the training." And
how long was the gap between 5 and 6? I heard it was a year and I also
heard it was 4 years.