Well there are a few places you can find guides for certain heroes, but generally I like to find a guide for a specific hero here
Champion guides aside, I know there will be a need for certain basic fundamentals to playing dota.
1) Last Hit, this is when you are laning in a lane for creep kills and gold, its always good to practice this in AI mode on only getting the last hit for the creep, this will mean you getting the gold for the minimal effort and less exposure to enemy hero hits, if anytime you find yourself mismatch (say you are a melee champion against 2 ranged heroes then its time for you to request a change with a team mate)
2) Survivability, if farming the creeps is ok for you then the next thing to concentrate on is how to last long in a lane, firstly its getting the less amount of hits not only from heroes but creeps as well and its always good to carry a few tangos for you to heal (i prefer tangos over healing potions as the healing doesn't get dispel upon hits)
3) Awareness, this is somewhat linked to the 2nd point, you need to play attention to the map, if not to the team chat, if enemy heroes are missing then its time to be defensive and stand in the range of your towers, but if the whole enemy team is missing even the tower will not be about to survive a gank of 5 enemy heroes.
4) Ganking/Leveling, this is when you have farmed enough for your hero and its time to bring the fight to the enemy team, its always good to appear like you are returning to base but heal using your potions/tangos and gank another lane's enemy heroes.
The basics are above and the rest you need to customise with heroes you are interested in, reading more guides will not only let you know what builds you can go but also the abilities of enemy heroes that you face.
Good luck in Dota 2