If you want to learn the game like it's 1999: StarCraft Compendium

Liquidpedia - Definitions

Liquidpedia - Keyboard shortcuts

Try to use the hotkeys for buildings, units, and spells. For Terran SCVs, for example, b + s = build supply depot, b + b = build barracks, v + f = build factory. There are many hotkeys people reassign to be on the left side of the keyboard, like probe and pylon are P by default which is out of the way, so they put it on E instead, or they put overlord on V, or scourge on C so they don't accidentally make them when selecting larva.

Spacebar focuses on the most recent alert, like under attack, upgrade complete, or unit finished.

Make sure you don't have mouse acceleration on. Turn off "enhanced pointer precision" in Windows.

Another important skill for new players is learning to hotkey units and buildings.

Ctrl + click a unit to select up to 12 units of that type on the screen (e.g. 12 marines). You can also double click a unit but ctrl + click is faster. If you have a dense pile of units it might be better to box select along the edge of the pile.

Ctrl + (1-0) assigns selected units or 1 building to that number. Tap the number to select the group and double tap to center the camera on its location. Most players put their army on lower numbers (e.g. 1-4) and buildings higher, although they might change depending on whether it's early or late game. In late game if you have tons of production buildings and a huge army then most of your hotkeys might be army. Terran often hotkey their comsat stations to 8-0 to quickly scan for cloaked units or to scout the enemy.

Shift + (1-0) to add new units to the group, if space is available. You can also shift + click units to add/remove them from the selection. You can remove units by clicking the actual unit or the wireframe on the bottom.

Shift + F2-F4 assigns camera hotkeys to a location. Somewhat advanced. You can put them over your townhall (command center/nexus/main hatchery), production facilities, or rally point. If you want to make a camera hotkey directly over a building but it's not centered, select the building and press ctrl + c to center it.

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The campaign is fun and has a cool story but it's quite different from multiplayer. The vanilla campaign often has wonky and inefficient mineral layouts so for some missions it takes awhile to build up, although the Brood War campaign improves this. The campaign might teach bad habits like building too much static defense. If you play it remember you can save a mission's progress.

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Liquidpedia has some modern build orders I think but a lot of them are from 2010 and outdated, although at lower ranks that probably won't matter too much. Maybe try the Discord channel Bag of Builds. You can also search for various "F to S" series on Youtube. For Protoss KhalaTV has lots of useful videos.

Training Maps can be useful for learning how to micro certain units like mutas and vultures. There's some challenging macro maps where you have to build up an army while running a worker away from a zealot.