You can share resources, ally chat, or give ships in a multiplayer game by using the Communications Menu (third button to the left at the top right of the screen). To be able to give vessels or trade resources, the option must be enabled in advanced settings, before the game has begun.
Once in game you can select how many resources you wish to give in increments as low as 100 for Dilithium or Tritanium and 10 for Supplies. To give resources to a player you must check the appropriate arrow which points to the particular competitor. In order to give ships you must have selected the vessels before pressing the “give units” button. You cannot share limited units, or any buildings or civilian vessels (construction and mining ships). You also cannot share any units or resources with enemies.
In most team games players will request (or will assume) that you have secured your communications so as to prevent plans from being overheard. You can select who you want to talk with by either using the preset toggles located at the bottom of the communications menu, or by manually checking the appropriate boxes under the “Chat” heading.
In multiplayer Alliance games you can also change your stance (neutral, ally, or enemy) towards each player in the game using this menu. The “Allied Victory” button is related to this type of game. If it is selected and all allies survive to the end, then the game ends with their victory. If on the other hand “Allied Victory” is not selected, then victorious allied players must defeat each other once their previous enemies have been destroyed.
You might have also noticed the “High Latency” button. When selected, all players will get higher response and execution times (aka lag will increase), however the game will become “smoother” (less frame stuttering). Consequently, in games that have slow response times to begin with, this option should not be turned on, as lag will become far worse.