A juice calculator is hard to explain kinda, but it makes itself clear once you identify one you like and just look at it... You input a target mix (e.g. each flavor %, how much VG and PG you want, how much nic (you'll have to input the nic base (VG or PG or a combination) and etc. It asks you to provide what you "want" and then kind of works its way backward, telling you how many ml/weight (depending on if you want to mix by weight or by volume, many folks start out using volume first) and etc.
As far as recipes you have options. You can use one shot flavorings in the beginning to get some "easy" mixing under your belt, you can attempt various recipes for flavorings that are created by others, or your can build your own by testing flavors singly to get a sense for steep time and make your own recipes. I did the last one (and kept some flavored eliquid around as I was building my skills) and would combine flavors in my tank (not the exact same as steeping together, but it gave me a sense of how things worked). I also tasted a lot of commercial liquid to get a sense of what I liked and hated, and I READ a lot of recipes but really wound up creating my own.
Whatever route you go, keep asking questions until things get clear and write down everything you do. Nothing worse than creating the "perfect" recipe and realizing you can't recreate it.
Also, it takes time to adjust to your own creations, so expecting some failure is often better than thinking "I will be successful right out of the gate." It's a lot of fun, and the more you do it, the more recipes will "build on" each other and your skills will increase. Keeping my expectations low to start was helpful (for me).
Best of luck and happy mixing!
Anna