Limonene smells like the tangy component in orange or mandarin. If you've ever smelled fir trees that have a smell reminiscent of orange, that's limonene
It is often said that citral "smells like lemons", but actually citral has the antiseptic/astrignent component smell of lemons, like the smell over a glass of water right after old bottled lemon juice has been. In high doses it almost has a eucalyptus-like quality to the smell.
Terpinyl methyl ether smells a little bit reminiscent of artificially orange flavored soda. Maybe it smells a little like the sweet light note of grapefruit also.
Myrcene is the scratchy resinous (floral in a way) aspect in pomelos.
Ocimene in the deep earthy (also resinous) aspect in the peels of Satsuma mandarins.
The pleasant green woody background aspect in grapefruit and pomelos comes from nootkatone (and probably some closely related sesquiterpenes).
The dry aspect in bergamot comes from linalool, also the main component in the smell of lavender.