Personal Tricorder is an incredibly important tool. New players always start with it. Even if you lose it, you have a spare Tricorder in your Ship Locker. You can also craft and/or buy a replacement.
Features
Shift + left-click
Holding Shift and left-clicking opens Research interface (here you "unlock" the recipes to craft new items).
Left-click
Left-click opens a menu with:
Information about player, bonuses/penalties of the chosen race, temporary immunities, etc.
GPS: information about current planet: its weather, gravity, surface biomes, surface dungeons, etc.
Tool to replace weapons, thrusters, etc. on your Mech.
Tool to upgrade all weapons/armors (for Upgrade Modules, up to tier 6) and tools (for Manipulator Modules, to the maximum tier that the tool supports).
Codex reader (it's more convenient than usual codex reader of Starbound, and also doesn't truncate long pages).
Right-click
Right-click opens the list of Tutorial quests (you can accept these quests in Tricorder without going to any NPCs). Not only can they be a guidance to new player, they also have some good rewards. It's a good idea to sometimes check if your current situation (discovered resources, etc.) allows you to complete some of them.
Shift + right-click
Tricorder also allows to configure the Matter Manipulator (hold Shift and right-click):
temporarily reduce 5x5 mining area (e.g. to 3x3 or 2x2) when you are building delicate houses and don't want to accidentally remove the blocks that you don't intend to remove,
temporarily replace some functions of your Matter Manipulator (like Paint or Scan) with some other tool or weapon (e.g. Gravity Wand or Void-Warp Locus).
The Quickbar (if you have either Stardust Core Light or Stardust Core mod) gives fast access to its primary and secondary features, but not its MM Config features.
Gadgetry (Engineering tree).
