The rule is simple: when writing a longer text, use the Space bar after each word and at the end of every line. If the line is too long, the text editor will automatically wrap the word to the next line.
Press Enter only when you deliberately want to start a new line - for example, to end a paragraph, create a list, or insert a blank line.
Using Enter at the end of every line is a habit left over from typewriter days. In modern text editors and browsers it causes formatting problems - the text won't scale correctly across different screen sizes.
Insert a single space after a full stop, not two. The two-space convention is a relic of the typewriter era, when a period was the same width as every other character. Computer fonts already build in the correct amount of space - two spaces just stretch the text out unnaturally and look unprofessional.
Tab is for indenting text - at the start of a paragraph or to build a tabular layout. Don't use multiple spaces in place of Tab: the visual width depends on the font, and the indentation won't line up correctly. In forms, Tab also moves the cursor to the next field.
Caps Lock locks the keyboard into uppercase, but in practice it's more often a nuisance than a help. It's easy to enable accidentally and start typing in ALL CAPS without noticing. For single capital letters, use Shift. If you do need several capitals in a row, turn Caps Lock on and off again the moment you're done.
Backspace deletes the character to the left of the cursor - it's what you use most often, to fix a typo right after making it. Delete erases the character to the right of the cursor - handy when editing existing text and the cursor is already in front of the character you want to remove. Both keys are handled by the right pinky.
To capitalise a letter, hold Shift with the opposite hand to the one pressing the letter. For "A", hold right Shift; for "L", hold left. This splits the work between both hands and speeds up typing.
Watch out for how Enter behaves in messaging apps. In most of them (Slack, WhatsApp, Discord, Teams) plain Enter sends the message and Shift+Enter inserts a new line. In text editors it's the other way round. When you start using a new app, check this first - accidentally sending an unfinished message is an awkward mistake to make.