The timing chain tensioner has a plunger in the center. You need to start taking apart the tensioner until you can push this plunger toward the engine end and out. You then take the plunger with the ratchet teeth and start it through from the "away from engine side. Since it ratchets, once the oil pressure builds up it will ratchet into its proper place.
To put on the upper timing cover, get the correct sealant fromt the dealer. This sealant is very slick when wet, so that you can push the cover in place without disturbing the u shaped seal at the bottom. Put the new seal in the cover, dob this sealant on the u seal and around the cover mating vertical surfaces. Then, put the timing cover down against the u seal and start moving it rearward. Use your fingernail around the shaft while putting slight pressure rearward. The fingernail is used to see that the shaft seal goes over the shaft without folding the seal. There is a special tool for this, but your fingernail will work fine. Once the seal is over the shaft push the cover rearward into place and start all bolts, then after they are all started, snug them in place.
Hopefully you noticed the small cups in the ends of the valves. Be careful not to lose any and put them carefully in place.
When laying the cam in place, put the rocker arm sets in place and start the bolts, then tighten each bolt a turn or so all the way down the line, then turn one turn or so again all the way down the line until they are all tight. If you just throw one rocker arm set in place and tighten down, you will strip the bolt holes in the head and/or break the camshaft.