You will need 1 command block, a pressure plate, and FUN!
Here's important stuff:
BE SPECIFIC. Command blocks are tricky. But there are a lot of functions.
@p will do the specified action to the nearest player
@r will do the specified action to a random player
@a will do the action to all players
Use regular commands BUT put the players affected after the command
Ex. /effect @p 8 1000 1000 Will gve the nearest player Jumpboost 1000 for 1000 seconds.
/

Step one: Place command block.
Step two: Open command prompt.
Step three: Type in command (/give)
Step four: Put in who will be affected. Ex. @p
Step five: Put in item ID, how much, strength, and all that stuff.
Step six: Put in data tags. {Use these whenever doing data tags}
Step seven: Put pressure plate in.
Step eight: Check to see if it works.
Step 8a: If it works, good job.
Step 8b: If it doesn't, you may have forgotten something or typed something in wrong.
Step 9: Fix it.
Step 10: It should work.
There! Your command block works.

Example commands: /say @p got 500 blocks of AIR.
/say Thank you @r for joining Minecraft Roleplay Server by Notch. JUST KIDDING!
/xp @a 1000L gives you 1000 levels of XP.
/tp @p 100 100 100 teleports the nearest player to x: 100 y:100 z:100

TIPS: Never do /(insert command here)
Try not to be overfrustrated.
Command blocks require a lot.

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