Professionals know what to do, they have all the contacts in place and takes the guess-work out of the equation.
But, if still you want to "learn" digital marketing in a week, I would suggest you start with Platforms - FB, Google,etc. Learn how to market there. Learn copywriting ads. Learn what kind of graphics work and what don't work. Learn from marketing gurus like Frank kern, Ben melol, Bredon Burchard, etc.
I took me 5 years of working with my clients to get to the level where I am contacted by unknown companies to do the marketing for them. So, I wish all the best with it.
It can be pretty fast for sure, but I feel it is something that is worth knowing for anyone who really wants to make use of internet marketing to push their products. So many things change and you would not need to be looking out every time for the agency but with the skills or recruiting someone with a good skills, is sure and much better.