A bankroll is the amount of money you set aside for gambling. It should be money you can afford to lose entirely, separate from bills, savings and anything you would miss.
Because slots have a house edge, a bankroll is best thought of as the price of the entertainment, not a pot to grow. "Bankroll management" cannot change the odds. What it can do is control how quickly money goes: smaller stakes mean less staked per hour and a lower expected cost for the same time.
Volatility affects how bumpy that is. A high-volatility game can empty a modest budget quickly before any feature lands, while a low-volatility game tends to wear it down more slowly.
Setting a deposit limit or loss limit with the casino turns the budget into something the account enforces. Never chase losses by adding more. If money for gambling is coming from somewhere it should not, see our safer gambling page or call the National Gambling Helpline on 0808 8020 133, free and open 24 hours.