You would need your recommendations turned in before the application deadline of the schools you are applying to.
Hopefully in your college career you've come had at least a couple of professors whose classes you've done well in and who might recognize you if you visited them in their office. I'm one of those kids who sits in the back and doesn't go to office hours but even I had a few classes where I got to know the professor well. If you don't think you have any, you better start building a relationship with some professor. What you dont want a professor to write is "I did not know this student that well, but s/he got an A in my class."
Now when I asked a professor for a letter I had everything ready for him. I had a folder with my resume, my personal statement, and a list of schools I needed him to send the letter to. For the schools that required emailed letters I gave the professors the address they needed to send it to. For actual letters I gave my professors envelopes with the address already written and stamped.
For me I had two pharmacist that I worked with write me recs and two professors one math and one science write me recs. I think A&M wanted 1 sci and 1 math so thats how I choose my profs. The pharmacists knew me really well so asking them was like asking a friend to write me a rec. For my profs I first asked over email if I could meet them in their office in their free time. When I met them in person I then asked if they would write me LOR's. I had my folder prepared if they did say yes. I basically reminded them who I was, why I wanted to do pharmacy, and how they would be doing me a big favor. There's probably a better way to approach it but I was pretty nervous at the time.
Even though your letter is technically due when your app is due, you want to do everything early. I think generally you want to give whoever is writing you a rec about month to do it. Everyone besides one prof finished theirs in two weeks, but still i gave them plenty of time and no pressure to do it. I started my app in mid october and had everything including recs done by late november/early december.
As for whats in recs and what they are composed of, beats me. I never looked at the prompts so I dont really know what it asks. I basically trusted whoever was writing to be able to understand and answer whatever was asked.