I don't wear perfume/cologne at all--I enjoy many scents, but there are so many people who are sensitive to fragrances that it seems rude (my SO can't stand perfumes, so I don't wear any anymore). I'd avoid it in crowds and offices, and recommend only wearing it if you're going to be spending time with someone that you already know enjoys it--otherwise there's absolutely nothing wrong with simply keeping clean. Most people smell pretty okay naturally unless they've gotten very sweaty/dirty or haven't washed in a long while. (Some people even prefer natural smells over perfumes.)

As for use: less than you think. Only you and someone in your "personal space" should be able to smell it. Don't spray it all over--use very small amounts on "pulse points": wrists, behind ears, throat. (This is harder to do with sprays than oils; it's easy to spray too much.) What kind: something you like. What smells good sprayed in the air in a department store may not smell as good along with your own natural scent, so you may want to test at home before wearing something in public. Ask someone at a department store or perfume shop to help you if you really have no idea what to get, and don't be embarrassed about it; if they are at all good at their job, they will be able to guide you toward scents of different types based on what you like--fruity, musky, floral, woodsy, light, heavy, what-have-you. If you don't know where to begin, think about other smells you like: fresh-cut grass, vanilla, ocean air, Irish Spring soap? If you have a significant other, ask what they like too...

(This is knowledge I have not used in a long enough time that I'd completely forgotten I had it!)