Overall most people tend to learn better this way rather than trying to learn all Excel formulas at the same time as this can be very confusing. Most of us tend to learn in smaller packages of information and you should look for a course of instruction that will allow you to do this. As you are learning to use Excel you should of course start by learning to use the formulas that you are actually using or are likely to have need of in the immediate future.
Build a solid foundation knowledge, you will find that all the programs upgrades is quite easy for you to understand. This is because the core foundation will not change. When it comes to learning new things, you want to take it one bite at a time. Don‘t punish yourself if you can‘t get it the first time. Don‘t give up easily. If you don‘t know how to even write an email, start by just register an account. If you don‘t have a computer, start by using the computers in the public library. Be flexible with the approach but be firm with the intention when it comes to learning the new technology.