Easy answer this:
Wear a latex or rubber glove and place a marble sized blob of the exhaust paste on your finger.
Rub the paste on the inside of the largest diameter pipe then simply place the smaller pipe inside.
With a gentle see saw motion left to right, wiggle the pipe further in until it resists going any further... Your paste will be now well and truly spread evenly.
Now get hold of a rubber mallet of a hammer and towel as protective padding if you don't have a mallet. start tapping with medium force on the silencer towards the join.... About three or four times will do.
Now lever on any supporting rubber bushes and inspect the exhaust for fit, making sure that you move the whole exhaust system up and down and side to side to check for possible contact against body work, heat shields or cross members.
Once you are happy, one last tap with the mallet.
Now put the U clamps into position with the nuts downwards for easy access in the future.
Tighten with your finger both sides equally and then proceed with a ratchet /socket to tighten two turns at a time on each nut to ensure it goes on evenly. once you have it reasonably tight and you start to feel that you are having to use a medium amount of force .. STOP, it's now tight enough... Let the paste do the work and not the clamps, it will pay dividends in the future.
I always buy the same size nuts and put an extra one on each bolt thread and nip them up to the face of the existing nut so there is no way that they will work loose
Start her up and wait for the paste to harden with the heat... Check for leaks, you will see tell tale carbon soot or if its a lot, you will feel the pressure on the palm of your hand....
Don't panic if that's the case, just apply some more paste to the leak without disassembling the clamp or joint and repeat the process of heating the paste up again.... Once the paste has hardened properly... Check the car a couple of days later and when the engine is cold, place your hand with a protective cloth over the rear tail pipe to temporarily seal the exit... You will feel back pressure but listen for hisses coming from under the car... Don't leave your hand on too long, just 5 seconds at most will do.
No hisses, great...
Any hisses, repeat the sealing paste process on the leak again until there isn't one... If you follow the above properly, you should never have to be at this stage anyway