For Bronze D of E you do 3 sections, each for at least an hour a week:
Volunteering - this is anything to do with helping the community for free; it can be on a local level e.g. helping out in a school club, or larger scale e.g. restoring a park or working for a charity
Skill - this is the vaguest sort of section; it's basically anything that's /not/ physical or volunteering :P
Physical - any sort of sport, dance or fitness activity; basically anything that requires a sustained level of energy and physical activity; you need to show improvement in this section e.g. if you're doing cycling then do longer routes etc
Timescales for Bronze are 3 months, 3 months, 6 months in any order. Most people do them simultaneously, but if that's a problem then you could do 3 months of physical, say, then 6 months of skill then 3 months of volunteering.
As far as I know I don't think you /have/ to complete the whole 3 or 6 months at once, but can repick up a section, but it might be worth checking
You do an expedition as well for 2 days and a night, but idk if you wanted to know abt that as much or if you were just asking about sections??
DofE's website is pretty useful btw:
http://www.dofe.info/en/content/cms/doing-your-dofe/activities-sections/Hope you do it though! I'm currently doing my Gold award and honestly DofE has given me some of the best experiences ever