I'm still in the kindergarten of this game and having touble with simple
trades, which don't happen. It took about 49 tries to hand the crypt
keeper his rat pie (finally threw it on the floor at his feet, which
didn't work either). Now I can't get off the raft. What am I doing
wrong?

Look down and click on the raft to disembark. To give an item, click the item button (one of the six small ones on the left). Then below the item there will be a "use" or "give" option, so click "give" then scroll to the object you want to give.

For giving items, you often need to get REALLY close to the NPC you're giving them to, even entering their polygons.

gee I wish we get some exp. for these side
quests like bilbows rat pie.

What you do get for the pie is a load more information. Didn't see ole Billibump the first time, so Rethpian didn't get his pie. This time I did the pie thing, and he gives out more information topics to select. The additional things : he says use bauble stick on crystal, use crystal on door, look for the secret chamber above Flokis Ra and hop on top of the lift. Considering a lot of people get stuck here, I imagine that Rethpian can't be getting too many pies.