Start with simple meals - all the big supermarkets have a freefrom range, so cereal or toast for breakfast, salad/ jacket pot for lunch, and something and potatoes/ rice/ gf pasta for dinner.
Easy dishes to make gf - curry, bolognaise, stew, sausages (black farmer , M&S, lots of other gf brands), roast, chops, chicken tray bake
Its overwhelming at first, but the good news is that all products have to declare the major allergens now, so take everything out of the cupboard, and start looking at the ingredients list and bin all the offending items.
Common places - stock cubes, gravy, soy sauce, ketchup, brown sauce, beans, oven chips, frozen roasties, crisps, tortilla chips.
Then go shopping with an online supermarket where you can spend plenty of time looking at the ingredients - I like Ocado as their specialist gf choice is really good and they list all ingredients generally.
Some gf pastas and breads are vile, some are OK. You have to experiment.
Start eating out with chains - most have menus online so you can think about the choice before you go, though all restaurants are now required to provide allergy info. Pizza hut, Dominos and Pizza Express all do gf pizza now.
Feel free to ask! I've been gf for 17 years now, and I still remember spending 4 hours on my first shop..