Minecraft Forums

Scoreboards are basically "variables" for players or entities. These allow you to keep track of scores (variables) for entities. I'm skipping teams for now. Basically you got objectives, which is a variable name. If you create an objective, you create a new variable, that is unset for all entities (unset =/= 0). Then you can edit this variable for every entity.

So, how to create a new variable (objective). You need to make something like this:

/scoreboard objectives add <name> <type> <Display <name>

Ok, that's overwhelming. What are we doing? First, we tell minecraft we're working with scoreboard. Then we're creating/removing objectives, not setting variables, so we type objective. We want to add one, so we type add. Then we need to choose a name, and set a type. Type is usually dummy, just a variable you can only edit by commandblocks. Other types include stuff like killCount, deathCount, Health and stuff like dead. You can find those on the wiki, it's pretty self-explanatory.

So, we got an objective. Great. Now what. We can now set this objective for certain entities or players. For that, we need to do something like this:

/scoreboard players set/add/remove @e/@p/Rubisk <objective name> <amount>

So, again, we're selecting the scoreboard, and going to players this time, to tell MC that we're working with individual players (entities) this time. Then we can do 3 things. We can set a variable, add a certain amount, or remove a certain amount. Then we need to select our entity, using @e, @p, or a name/UUID. Then we give the name of the objective to edit, and then the amount.

So, we can link variables to entities, and keep track of scores, but now what? What can you do with that? Well, we can actually check for these scores too, after we've set them. In the [] brackets after @e/@p, we can add two things:

 @e[score_Variable=1], @e[score_Variable_min=0]

The first one checks for entities with the maximum score of 1 (not a score of 1 (!!!!!). The 2nd one for a minimum score of 0.

So, we can create objectives, set them for entities, and then track those entities. Pretty usefull, but where does the dataTag come in?

Well, we can use datatags if we set variables for entities. Like this:

/scoreboard players set/add/remove @e/@p/Rubisk <objective name> <amount> {datatag:x}

Some notes:
using

/scoreboard objectives setdisplay sidebar <objective name>

you can keep track of all scores for players/entities for that objective, for if you have trouble finding out why stuff doesn't work.

If you don't set a score for an entity to a value, trying to find it with @e[score_Variablename=x] won't work. It's not considered 0, it's considered NULL (No value). That's a bit of a coders thingy.