What it means
To give someone the boot means to chuck them out or fire them. Could be from a job, a pub, a group chat, wherever someone's decided you're finished and the door's got your name on it. You also hear get the boot when you're the poor soul being binned off with no big ceremony.
Usage examples
"Dave got the boot for rocking up late again with a lukewarm Greggs. Manager went, nah mate, you’re done, and even the bouncer sighed."
"My nan gave the boot to her bridge club after one too many smug comments about her sandwiches, set up a rival club in the church hall and stole half the original members."
"The new manager gave Dave the boot on his second week for putting decaf in the proper coffee jar, the office cheered and somebody actually baked a sponge cake by Friday."
"He gave Tom the boot after that mad email-all rant, and by lunch everyone was pretending they hadn't liked a single one of his jokes."
"Got the boot from the five-a-side WhatsApp because I missed two matches and called the organiser a tiny little dictator. Fair enough, probably."
Where it comes from
This phrase is recorded in English from the 1800s and grows out of the literal idea of using a boot to kick someone out. That rough image slid from physical ejection into figurative use, so by later slang it could mean getting thrown out, dismissed, or dumped from somewhere sharpish.