What does a possible command look like if I want you to be on a specific block such as Want to damage 0.5 hearts per second?
Ps. I have no idea about commands.
/ execute at @a if block ~ ~ -1 ~ minecraft: white_wool run effect give @p [distance = .1] minecraft: poison 1 4 true
This means that every player who loves white wool gets damage (version 1.15)
Do you write that in a normal command block?
Yes, but a clock must then be connected to the command block or the command block is set to repeat
In a repeat command block (the blue one)