As widespread as feminism seems to be, out there in the real world a lot of people just don't seem to get it. On the occasion that I go off one one of my rants, whoever I'm with will (usually) agree with me, but when I ask if they're a feminist, they'll get all cagey and evasive, 'Well, I don't know if I'd go that far...' Let's put it simply. Feminism = Equality. Once you get that round your head (take as long as you want) you're well on your way to joining the movement.
I've always been a feminist at heart, but only really discovered there was a word for it once I spent a while on the internet. I don't think there's any shame in admitting that tumblr taught me a lot - I just advise not to take everything you read about feminism on there as gospel. Tumblr is a place to indulge your obsessions - some people will gush about how much they love Game of Thrones, others will scream abuse towards all white men in the name of feminism.
|Look! You can be a white cis man AND a feminist! Crazy, I know.|
A lot of people have a hard time getting their head round this - even I slip up sometimes. If you question why a fat woman is wearing a particular item of clothing, it doesn't make you a bad person - as long as you realise and correct yourself. Recognise that our standards of beauty are being perpetually manipulated by the beauty/diet industry. White skin, blonde hair and an hourglass waist aren't the only measures of beauty!
If you're confused as to why someone has a feminine name when they appear masculine to you or vice versa, realise that it's not really any of your business. Recognise that just because someone doesn't meet your preconceived idea or image of a 'woman' doesn't mean they aren't one. (This also goes the other way. Saying 'omg i would never believe you're transgender, you're so pretty!' could be taken as a compliment, but is also pretty offensive.) If you're friends with, or meet someone who is genderqueer, all you need to do is ask them how they prefer to be addressed. If they don't disclose their pronouns, just refer to them by the neutral 'they/them' - it's really not that difficult.
Sometimes realising your privilege is really important because you can use your voice to help marginalised groups. However the most important part of being an intersectional feminist and ally is making sure you don't speak over people or drown their voices out. (eg. If you're white, you don't get to choose if something's racist or not.)
Basically it's just about being a considerate human being. Good luck!