Quick answer
What is gas, and why does it change?
What you're actually paying for, and when it's cheapest to move.
The long answer is still being written.
Other questions
Is USDT the same as Bitcoin?No — one tracks a dollar, the other floats. Who issues each, and why it matters.
What happens if I send to the wrong network?Usually the funds are unrecoverable. When they aren't, and what to check first.
Do I need a hardware wallet?Depends on the amount and how often you move it. A threshold you can apply.