This is what the slipcover will look like when fitting. It is easier to fit this way when it's inside out.
And this is the finished product...Hopefully! I recommend studying photos and look up "How to make a slipcover" on youtube. Ther are many to choose from that will suit your needs. If you have a slipcover already, turn it inside out, study it, get a concept of how you'll be piecing it together. You could even rip it all apart and use it as a pattern for different fabric if you aren't using it anymore. I've made many slipcovers through the years, so to me, this is easy...but it took some guts to finally start doing it instead of procrastinating about it. I hope I haven't confused you any and I hope this will help a little.
Now go make a slipcover...no time like the present!