Search the forums, this has been discussed *multiple* times:

https://forums.sinsofasolarempire.com/347562

https://forums.sinsofasolarempire.com/347777

https://forums.sinsofasolarempire.com/344728

...

Here: 'list of tips' that appear during loading screen.  Compliments of the SoaSE wiki.

• 00 Hold down 'Alt' on your keyboard to quickly see health bars, tactical grid, attack ranges, unit orders, and more.
• 01 Pirate raiders and local militia favor colony ships as targets, so be careful when bringing one into a contested system.
• 02 Your first capital ship will be built for free, every one afterwards will be full price.
• 03 Capital ships stationed around friendly planets will slow the spread of enemy culture towards it.
• 04 Bomber strikecraft are very effective at attacking structures.
• 05 You can configure your capital ships to automatically upgrade their abilities when they level up by right clicking the Ability Management menu.
• 06 To issue queued orders, hold down 'Shift' while issuing them. Movement, attack and ability orders can all be queued.
• 07 To force all your selected ships to Phase Jump together, enable Group Movement by right clicking the move button.
• 08 To see a per-planet breakdown of your income rates, hover over your resource amounts in the top right corner of the HUD.
• 09 Capital ships with available ability points will show a '+' near their empire window icon, and ships and structures with unassigned strikecraft squadrons will show a '>'.
• 10 Hold down 'Shift' to zoom the camera in smaller increments.
• 11 To hide infocards, ownership icons and other 2D elements in order to take cleaner screenshots, enable 'Cinematic Mode' with the button near the top center of the HUD.
• 12 To select all units of a certain type within a gravity well, hold down 'Alt' while selecting one of the units.
• 13 You can anonymously place bounty on allies you don't have a peace treaty with.
• 14 Pirate Raiders will attack the player with the highest bounty on them at the moment the raid is launched. Make sure it's not you!
• 15 Hold down 'Shift' to buy ships, structures and resources in larger quantities at once.
• 16 Chat with other players by pressing 'Enter'. You can change who you send messages to by pressing 'Tab' while typing.
• 17 You can scroll to old chat messages received by bringing up the chat window with 'Enter' and using the mouse scroll wheel while the cursor is over the message area.
• 18 'Caps Lock' will instantly change your camera to either a planet view or a galaxy view.
• 19 You can focus on game events by selecting their card in bottom left, then pressing 'Spacebar'
• 20 Building trade ports in adjacent planets will link them together. The longer the chain the more trade income will be generated per trade port. Hold the cursor over your credit summary to highlight your longest chain.
• 21 Refineries can exploit owned and adjacent resource asteroids. Asteroids can only support so many refineries at a time though.
• 22 Killing enemy trade or refinery ships will give you credits and decrease the unfortunate owner's rate of income until they are built again.
• 23 Enemy culture on your planets will decrease their allegiance. If planet allegiance reaches 0% you will lose control of the planet.
• 24 Friendly culture will increase your allegiance past normal levels.
• 25 Your maximum planet allegiance is based on the planet's distance from your home planet.
• 26 Planets with low allegiance will have lower credit and resource income.
• 27 Explore planets from their Planet Development menu to find valuable artifacts and other bonuses.
• 28 Completing missions for other empires will raise their opinion of you, eventually leading to peace offers and other treaties.
• 29 Unbuildable ships and structures will show a small icon in the corner of their disabled buy button. This icon hints at what you are missing to build them.
• 30 Some planet types require habitation research to be conducted before they can be colonized.
• 31 Ships produced from planets that are rallied to other ships will attempt to join the target ship's fleet if one exists and their auto join fleet behavior is enabled.
• 32 Ships who aren't in a fleet and who have auto join fleet enabled will attempt to join the best local fleet in their current gravity well. Disable this behavior by right clicking the Create Fleet button in the Tactics Management grid for each ship.
• 33 Capital ships can gain levels from experience earned by being present when enemy ships are destroyed in combat or by purchasing training for them.
• 34 Watch out for pirate Pillager ships, they can steal credits from your empire by targetting ships and structures with their Plunder ability.
• 35 AI players can be influenced if they are happy enough with you. If you complete enough missions, you will be able to ask him to attack or defend planets for you.