/effect
is quite simple

/effect (user) minecraft:(effect) (amount) (like speed 3 etc.)

so lets say we but the highest amount of speed but for ten seconds so it would be

/effect (user) minecraft:speed 10 255

its quite simple you can use this one in the chat

ill will be posting how to get a command block and a another one but its gonna be a secret but its pretty fun but kinda long

BYE HAVE A WONDERFULL DAY

and tell me in the comments what command to do next!