General
  Once you have registered an account at the matrix you have also created a profile and a channel.
Account
  You have one account. This consists of your email account and your password. With your account you access your profile and your channel.Think of your account as the way you authenticate at one Hubzilla site. It lets you do things, such as creating profiles and channels with which you can connect to other people.
Profile
  You have surely registered with some other internet services, such as forums or online communities. For all of them you provided some information about yourself, such as date of birth, country, age and the likes. Unlike other services Hubzilla offers you the advantage of creating many more profiles. That way you are able to distinguish between profiles targeted specially at everyone (your public profile), your work mates, your family and your partner.Think of your profile as the basic information about yourself you tell other people.
Channel
  During the registration you created your first channel. Yes, besides several profiles you are able to have several channels. This might be a bit confusing in the beginning, but let's clear things up. You already have created one channel. You can use this one for the public, to communicate with people about every day life. But perhaps you are an avid book reader and many people are bored by that. So you open a second channel just for the book lovers, where you all can talk about books as much as you like. Obviously this is a new stream of posts, with a new profile (... or new profiles ...) and completely different contacts. Some connections might exist in both channels, but there will be some that are exclusive to only one of both. You yourself just switch between both of them just like you would in real life switch when talking to people you meet on the street or people you meet specially to talk about books. You can even connect to yourself, or better: to your other channel. :)Think of a channel as different spaces dedicated to different topics where you meet with different people.