An octave is 8 notes, from "C" to "C" (this does not include the sharps and flats - black keys). A crescendo is where you are singing and progress to a louder sound- volume; decrescendo is where your singing gradually gets softer. The signs look like a "greater than" or "less then" sign in mathematics.
Pecker also gave some good advise... Start practicing with your guitar if you do not have a piano or have someone who can assist you. Match the tone with your voice. If you feel it is straining, then select another key to sing it in.
As for a cappella, unless you have perfect pitch I would not suggest you attempt this. A cappella does not give any room for error - it is pure blend of your voice and tone, nothing more. It is also very difficult to master...
Anyway, I still have not been able to hear your links but do wish you well in your endeavors. It seems as if a lot of people here are musically inclined or trained; I am certain someone will be able to offer you adequate advise.
Oh, did you try the exercises I mentioned? If so, how did they work for you?