how I go about starting & do you have to follow a curriculum?
You would need to deregister her from school (assuming you are in England and Wales, you just do it - there's a thread really close to the top of the home ed topic that gives you instructions. In Scotland it's a little bit more complicated). That's you started.
Usual advice is to allow a month of recovery for every year spent in school, assuming no major trauma, before starting to do anything that looks explicitly educational in any way (that period is called "deschooling" and is recognised in the Government guidance to Local Authorities about how to interact with home educators).
After that, no you don't have to follow a curriculum. Home educators encompass everything from people following the national curriculum, or buying a "boxed curriculum" (usually from the USA), through people who do an hour or less a day of reading writing and arithmetic, and let the rest happen through osmosis, through to the radical unschoolers who don't impose adult led education at all, but instead have interesting, creative and educational stuff around, and make opportunities available, and it's up to the child how and when they engage with any of that. Sounds crazy, but I have seen home educated children teach themselves (and each other) to swim without a single swimming lesson being involved, and that's the last bastion of "but they have to be taught how to do it" for me, conceptually :) I've certainly known lots of home educated children who ask for help with learning to read when they need it, and otherwise just get on with figuring it out when they have something they badly want to read
My biggest worry with HE is how do we develop her social skills/develop friendships with other children? Obviously if she was attending school she would make friends as she grew up but am worried once we start home educating her & as she gets older how friendships are going to develop?
OK, get yourself onto facebook. Search for Home education with your county name, the name of your nearest big city, maybe the name of your nearest big town (for us, the active home ed facebook communities are county, big city, and then the village where one of the meet ups happens, but you'd find that village group (which people go to in a 10 mile radius) by hanging out on the city or county facebook groups, yk? That'll give you a sense of what's going on in your area. I'm kind of hoping you live near me now, because you'd get such a shock when you logged on and realised that there are multiple HE activities you could join in with Every Single Day of the Week, and your problem with socialisation is actually going to be ever getting a quiet day at home :D