101 can be confusing and involve the use of a lot of terms and ideas you may not have encountered before. Here's a quick guide to some of them.

Privilege: Privileges are the invisible advantages that accrue to a person because of their gender, race, sexual orientation, religion, or intellectual or physical ability, education level, or socio-economic status or the like. Privilege does not mean your life has been easy, or lacked obstacles. It just means there are obstacles that other people have to deal with just because of who they are - obstacles you may never have noticed. Think of it as an invisible booster that makes it so you go a little further than someone who was exactly the same as you in every way that mattered, but didn't have that advantage. Here is a comic that is a good demonstration of the way a lot of these little advantages can add up. 

Racism: There are two different but related definitions of racism, something which can cause a lot of confusion. The simple and most common definition of racism is "the belief that other races are inferior". In the world of social justice, the word "racism" is mostly used to talk about systemic or structural racism. These are the systems, habits, perceptions that essentially enforce racism in our lives. In other words, a person can be very much against racism in the abstract sense (as a political belief) but still live racism. This does not make that person a bad person necessarily: racism is all around us, built deep into the fabric of society, and it takes a lot of work and effort to break free of its influence (and even then, it'll still be lurking). An example of this kind of racism would be the fact that black children are consistently perceived as being less innocent (and less worthy of protection) than white children of the same age and background. There are a number of studies that show this, and it's true even for people who would be horrified to realize they're doing so. That's the problem: that's a form of racism that's not a thought, but a deep subconscious perception. People do not even realize they're doing it, and that's what makes it so deadly. It's why black children are consistently treated with more force by police officers in schools, even over minor things. Even if the police officer isn't thinking, "this child is black, therefore they are less innocent," in that split-second judgement, they are perceiving them as more dangerous and less innocent, and that changes how they react. You can read more about structural racism (and related ideas) here. (link goes to a PDF)

If someone tells you that you're doing something racist, don't take that as being the same thing as telling you you're a bad person who believes in racial inferiority. Instead, listen to what they have to say and ask questions. Someone is telling you that you're hurting them or others, even unintentionally. If you stepped on someone's foot, and someone said "ow", you wouldn't argue about whether their foot actually hurt, you would step off and apologize. Try to embody that here.

Microaggression: This are those "harmless" comments that are much like backhanded compliments: they contain a hidden sting. Ever had someone say something like, "You're so brave, ordering a hamburger for lunch," as they make a big deal about ordering a salad? It's not really a compliment is it? Unlike someone being catty over your diet, microaggressions are often committed by people who aren't really aware of what they're doing - but that doesn't change the fact that they're often about enforcing the status-quo. The constant critiques of the speech of girls and women is an example of a microaggression - without meaning to, what it enforces is the silence of women. If someone suggests that something is a microaggression, don't get defensive: just like above, it's someone telling you that something you said has hurt them, whether or not you intended it to. You can read more about microaggressions here and here. 

Derailing: Derailing is a way of turning a conversation away from something, especially because it makes you feel uncomfortable. "All Lives Matter" as a response to "Black Lives Matter" is an example of derailing. By way of illustration, imagine if anytime someone said "Save the Rain Forest" someone said, "what about the wetlands?" or "Save all nature!" It's not that those other things are wrong, but it's not the point - and the only reason they're brought up is to stop conversation about the first thing.