I am pretty sure the burda patterns don't have instructions in the envelope. I think that you should start with a different pattern company. The simplicity company has redone thier patterns to make them better and easiler to use. I love the mcCall and butterick patterns the best because they have more detail to them. The way you determine your apttern size is by measuring youself carefully in the areas that are required for the garment you are making. Now, remember the patterns are standardized. You might have to alter the pattern slightly for it to fit you well. Just take a tape measure to the height and width of the pattern and make small adjustments to it. Remember to figure in ease so you can move it it right.
Well, there is a little bit of a learning curve to anything, right? Just don't buy a pattern that is too advanced to start out. Keep it simple lines and I think you will do fine. Don't forget to check the pattern for any notions or thread that you need to make it and get them while you are there at the fabric store. Give yourself time, don't rush it. I finally broke down and bought an adjustable maniquin to work with. I love it!