Here is the best shorthand interpretation of what this story is about in a nutshell.
He was thrust into the past with the help of Doom's time machine. That was done in an attempt to wear Cap down from fighting all of his enemies again. Throughout the process he has to relive all his highs & lows all over again without changing a thing for fear of some unwanted event happening. Now Red Skull has been transferred to Cap's body, thinking that Steve Rogers conscience/essence (whatever you want to call it) has been suppressed by Armin Zola with the help of him having to relive his rocky past. However Cap has started to fight back...
Yes... it is silly I know. Silly beyond belief.