Welcome Rose.
Starting with a clean slate is challenging.
One good source of info is a reputible bike shop. If you need help finding a good shop let the forum (us) know what area you are in and I'm sure someone can help direct you to one. If you live in a metro area there are probably several shops you could visit. Local cycling clubs are also a good source of info.
There are some specific cycling clothes you may want to purchase. Shorts are very helpful, and tops made of a wicking fabric like coolmax are more comfortable in the hot weather. Helmets, gloves and shoes are available and will probably increase your comfort and safety level.
There is a wealth of information on the web; Retailers, forums, clubs, periodicals.
It helps to have specific questions or goals. Doing 75 miles by August should be a breeze.
Do you have a bike?
What is your current fitness level?
Do you have access to trails or safe roads to ride?
Do you know anyone in your area who rides?