What exactly are Expanded Spell Slots. Do they effect spells known? I'm very new to D&D, and I am unsure what it means. I did look in the PHB, and found this:
The Warlock table shows how many spell slots you have. The table also shows what the level of those slots is; all of your spell slots are the same level. To cast one of your warlock spells of 1st level or higher, you must expend a spell slot. You regain all expended spell slots when you finish a short or long rest.
For example, when you are 5th level, you have two 3rd-level spell slots. To cast the 1st-level spell thunderwave, you must spend one of those slots, and you cast it as a 3rd-level spell.