Heres a photo of the plant.
thanks

It's a Rhipsalis, probably R. ewaldianna, although R. sulcata is very similar. Rhipsalis are epiphytic cacti, closely related to the Schlumbergeras, or "Christmas cacti", and very easy to care for, but the whole taxonomy thing with this genus is a mess, and there are many species available commercially that are not correctly ID'd, and even among experts in the genus, a positive ID of a plant can be difficult. In any case, you care for this plant as you would a Christmas cactus-filtered or medium light, keep slightly moist soil in the growing season and allow soil to dry out between waterings in the winter off-season. I collect Rhipsalis myself and have a large specimen of this same plant which was labeled as "Rhipsalis ewaldianna" by Exotic Angel Plants(purchased from Lowe's). I actually keep mine over the winter on an enclosed, but unheated, back porch, and temps have reached the lower 20's F. out there, with no apparent ill effects to the plants. I would not recommend exposing them to frost, though, or to temps below that.

But what is the stuff on it?(see first photo) Is it a fungus? Bugs? Bird do do?

S.A.McKenzie thanks for the ID.

I dont think its a case of what's on it, more of whats in it! Looks like burrowing grubs have made a home there. A similar thing is often seen in holly leaves, caused by leaf miners.

oh dear, should I return the plant? I dont want my other plants to get what ever it is.

You can return plants? I dont think that would work over here!

Could it be fungus? read fungus/diseases
http://cactiguide.com/cactipests/
I did find some red fungus looking stuff in the soil.

Oh yes, we can return any plant as long as we have the receipt.Outside garden plants are guaranteed for 1 year. If they die, just take the receipt to the store and tell them. Although I usually dont bother for outside plants.

Patches of sunburn where water droplets had been, maybe?

could be amccour but there were also orange things in the soil. I am starting to think fungus.Also I see now some of the branches look dehydrated, even though the soil is very wet.

I returned the plant, I didnt want to take a chance.