white bits on tree bark
 

I have a flourishing tree and it is now quite large. I do not know what kind it is.
How do I identify it?
What are these little white or gray spots all over its bark? I have seen birds occasionally eating them or so it seems. Also under the tree which hangs over the patio, everything seems to get sticky. Thsi is not too pleasant when it falls on the cushions etc.
Are the white marks some kind of fungus? Are they curable? The tree seems to be totally unaffected by them!!
Any ideas would be a help
Thanks,
Andrew