Setup guide
Everything a host needs, in the order you will actually do it. A first tournament takes about ten minutes to set up, then a few seconds per match.
Sign in and make the tournament
Open the admin and sign in with osu!. Create a tournament with a name and an acronym. The acronym becomes the web address, so AC6 gives you /t/ac6.
Pick the format now: Team with the number of players per side (4 means 4v4), or Solo for a 1v1 tournament. Solo has no teams at all, so the player list is just osu! ids and the public page hides the team tab.
Set the win condition too. It decides who wins a map: accuracy or score. Every stage follows it unless you change that stage on its own.
Add the players or the teams
In a solo tournament, open Players and paste osu! ids or profile links, one per line. Names are pulled from osu! for you.
In a team tournament, open Teams and rosters. You can add teams one at a time, or paste the whole list at once, one team per line, as the team name followed by the osu! ids of its players.
Put everyone on the roster, including subs. A player who is not on a roster still gets their scores read, but the site cannot tell which team they played for.
Create a stage
A stage is one stats page, so it can be a single round or a few rounds grouped together, like Swiss weeks 1 and 2. Give it a name and, if it is a qualifier, tick This is a qualifier.
A qualifier works differently: one lobby holds many players or teams, everyone plays the same maps, and no map has a winner. If your qualifier runs through the pool twice, say so on the stage and choose whether the best run counts or the two runs are averaged. One run is the normal setup and the default.
Paste the mappool
On the stage, open Mappool and paste the pool: one map per line, the slot name and the beatmap link or id, like NM1 1234567. Titles, covers and star ratings are fetched from osu! automatically, with the mods applied.
Add the matches
Open Matches and paste the MP links, one match per line. If a match was split across two lobbies, put both links on the same line. In a qualifier, one line is one lobby.
Maps that are not in the pool are treated as warmups and left out of the stats, so you do not have to clean anything up first.
Review, then approve
Each match opens with a list of anything that looks off: a missing score, a player nobody has on a roster, a map played twice, the wrong side. Fix what needs fixing, then hit Approve. Nothing shows on the public page until a match is approved.
Publish it
A new tournament is unlisted, so only people with the link can see it. When you are happy with it, go to Settings and release it to the public list. You can also set a banner image there, and add other hosts as managers so they can help.
Loaded the matches before the players or the mappool?
That is fine, and it is a normal way to work. Scores are matched to players and to mappool slots at the moment you paste the MP links, so anything you add later is not picked up on its own. Go to Settings and hit Refresh to redo that matching: on the tournament for every stage, or on a single stage. It is safe to run at any time and never changes scores, warmup marks or bans.