Minecraft wiki entry for execute, associated text: Modify subcommands modify command variables and change the situation the command is executed, and execute subcommands following it with specific executor(s), execution position(s), execution dimension(s), execution rotation(s) and execution anchor.
Condition subcommands are used to test whether certain conditions are true and output results or limit conditions of execution.
Store subcommands can store the return values of the command in a scoreboard or the data of an entity, block entity, or storage, and can also change the maximum or current value of a boss bar.
run subcommand is used for carrying out another command.