1.
You can do each raid once a week. If you have already done it you will be "alone". That is because when you kill first boss you and everyone else in the same raid group recieves specific "lockout ID". When you have this ID, you are "SAVED", you will be able to see only people with the same "ID".
These "ID"'s reset on specific day at a specific time, so it's not "resets after 7 days from the moment you are saved". It's something like Thursday 6:00 Server time.
Press O > Raid > there will be a button on top, it shows all your lockout IDs and duration.
2. Usual loot distribution is done by rolls. Leader says "Roll [stuff] main spec!", and if that item is appropriate for your main spec you just type /roll
by reading your answer, an other question comes to me about the "SAVED" we are alright that the ID block only on the same raid with the same players and difficult?
Example: if i play TOC10 NM can i play TOC10 HC, TOC25 NM and TOC25 HC without resets?
Raids are split into 10 and 25, you get separate ID for each.
Ulduar had "Hard mode", as an actual ingame condition to activate it. Still there is only 1 "25man" ID, regardless of how you kill bosses.
Then came TOC, which introduced sort of "changeable" difficulty. So you get 4 separate IDs. Probably they realized there are only 5 bosses to kill until next patch lmao, so they stretched it out to 20 bosses.
After that they realized that's too generous and ICC/RS has only 2 IDs again - 10man and 25man, doesn't matter on which difficulty you do it.
Malygos (Eye of Eternity) 10
Malygos (Eye of Eternity) 25
Ulduar 10
Ulduar 25
Onyxia 10
Onyxia 25
Trial of the Crusader 10 Normal
Trial of the Crusader 10 Heroic (Real name would be Trial of the Grand Crusader)
Trial of the Crusader 25 Normal
Trial of the Crusader 25 Heroic (Real name would be Trial of the Grand Crusader)
Icecrown Citadel 10 Normal and Heroic
Icecrown Citadel 25 Normal and Heroic
Ruby Sanctum 10 Normal and Heroic
Ruby Sanctum 25 Normal and Heroic