From Halopedia, the Halo wiki
The main menu is a series of menus and lobbies that players interact with in all Halo games.
The main menu is reached after a series of logos for the companies that produced the game and a splash screen. Sometimes the music of this sequence leads into the music of main menu itself. Examples of this are in Halo 2 and Halo Wars 2.
Upon reaching the menus and lobbies, one can access a number of gamemodes, settings and options, and view the Message of the Day (MotD). The Season is also often shown in the menu too. In the options section, one can change their control schemes.
The gamemodes that can be accessed through the menu include campaign, multiplayer, firefight, Spartan Ops, Warzone, Custom games, Theater, Forge, and File Share. Downloadable content such as new campaigns are often directly accessed through their respective lobbies or areas of the menu.
In most games, the ability to change one's Armor permutations and armor effects is accessed through the main menu in some form. So to for Skins for weapons and vehicles as well. In Halo: The Master Chief Collection, The Exchange is only accessed through the main menu.
Halo: Combat Evolved
The Halo: Combat Evolved menu is set in orbit of Installation 04, with the camera rotating and moving about it showing its interior, the exterior shell, and Threshold. The music heard is Halo Theme and the final part of Brothers in Arms.
The menu of Halo 2 features a background of the Solemn Penance, next to the Mombasa Tether in Mombasa, East African Protectorate. The music heard is the Gregorian chant in Prologue, Ghosts of Reach, Heavy Price Paid, the last minute of The Last Spartan, and Unforgotten.
The main menu of Halo 3 features an animated view of a cliff at the edge of the Portal at Voi with several Covenant starships circling it, and Banshees patrolling over it. Movement, Never Forget, Choose Wisely, the beginning of Honorable Intentions and an unidentified choir track will rotate as the backing music.
Halo 3: ODST
Halo: Reach has a variety of lobbies all using their own artwork(s). The music used in the lobbies is Overture, though sometimes no music at all will play and instead, the sounds of distant gunfire and other fighting will play.
Most of the artwork used in the various menus and lobbies of Reach were actually pieces of concept art created by Isaac Hannaford. Depending on the lobby, the artwork would be different. As well, the artwork on the main menu would be different depending on which campaign level(s) were last played.
Halo: Combat Evolved Anniversary
The main menu for Halo: Combat Evolved Anniversary was designed very similarly to the original Halo: Combat Evolved menu. When selecting multiplayer however, the menu was change to one more designed like and using from Halo: Reach.
In an alpha menu, the background was to be the broken planet around Installation 03. Two versions of To Galaxy were to play; one of just the strings used in the song and the other of the background electronic "drums" as well as an unknown track that was later used in the Halo 4 epilogue, Halo 4 lobbies in Halo: The Master Chief Collection, and at the beginning of the track Blue Team in Halo 5: Guardians.
The released main menu is of a debris field around Requiem. When reaching the title screen and for a time in the main menu, Atonement will play. It will change to Wreckage then the first minute or so of Green and Blue and rotate through all three while on the menu. When Infinity multiplayer lobby is selected, the image will move into the bridge of the UNSC Infinity where the first minute of To Galaxy will play on repeat.
Halo: The Master Chief Collection
Uniquely, depending on the lobby for which game that will be played, the menu music for that game will be played. Uniquely, for Halo 4 lobbies a new track was added. This being the unnamed Epilogue track (used in the early Halo 4 menu and the opening for Blue Team).
Similar to Halo: Reach the background artwork will change in various lobbies depending on the selected game. On top of this, depending on the Season currently going in game, the main menu background will be different.
Halo 5: Guardians
In the Halo 5: Guardians Multiplayer Beta, the menu was set in an orbital facility of some kind (the skybox of which is used on Breakout Arena) with SPARTAN-IVs, Naval personnel, and scientists at various computer and hologram stations.
The menu consists of a profile shot of the UNSC Infinity in orbit of an unknown planet. Various UNSC starships and dropships will fly by, dock or move about the Infinity. These include Anlace-class light frigates, Winter-class prowlers and D79-TC Pelicans.
When getting to the start screen and for a time afterward, Halo Canticles will play. The music will then rotate through Rock and Ice, about a minute of Blue Team, Dominion, the first minute of Jameson Locke, about a minute of Osiris Suite, Act 3, and two minutes of Osiris Suite, Act 4. After returning to the menu from playing a multiplayer match, On Deck will play.
Halo Wars 2
The menu is composed of a tableau scene of several units from either the Banished or UNSC. The menu background is chosen at random upon the game's launch. The music heard in the background is Cratered.