A lot of people just associate OCD with the typical "germaphobe" type thing, but it's absolutely not just that - OCD is very complicated and can manifest in a great, ... possibly infinite number of ways. These are just some of the typical compulsions:

• Rumination
• Seeking reassurance
• Cleaning/Tidying
• Checking
• Verbal, mental, or physical compulsions, such as mantras, numbers, words, or movements
• Hoarding (I think this is one, ... some argue that hoarding doesn't belong as an OCD sub-type, but I disagree)
• Improving, updating, upgrading, bettering, perfecting, etc

... and many more.

As for the obsessions:

Some can become obsessed with the idea they are bad, evil, gay, lesbian, sexually inappropriate, violent, or that they need to do their compulsion in order for something bad to not happen. Some people become obsessed with health, although this tends to touch on hypochondria and/or "health anxiety", but I believe it to belong as an OCD sub-type, given there are clear obsessions and compulsions. There are people that are obsessed with perfection, such as perfect grammar, perfect speech, perfect placement of objects, perfect food, and so on.

There's really a lot of these, too.

OCD = Obsessive Compulsive Disorder - the sufferer obsesses, and as a result, is compulsive, which causes disorder in their lives, be it social, work, education, or otherwise.