Yes, Bet365 is safe to use. The sportsbook provides various levels of firewall and other protections and the sportsbook itself is regulated by each of the state gaming regulations Bet365 is legal in.
Log in to your Bet365 account and select the 'Sports' tab. Select the markets of your choice and add them to your bet slip. Make sure you have at least three selections, as this is the minimum required for an accumulator bet. Once you have added all your selections to your bet slip, select the 'Accumulator' option.