Blocks are a powerful tool but must be understood.
Block is a generic term inappropriate for learning
A block can be a definition or an insertion.
To use "blocks" you can define a block (block definition)
then you add in the drawing a entity "insert" (block insertion)
referencing a "block definition".
A "block definition" is like a group of entities, it can contain all
type of entities (lines, arcs, "block inserts", text...) and the entities
forming a "block definition" can be in any layer and have any
color or linetype.
A "block insert" is like a point, is an entity with its layer, color and
line type but when it is drawn shows the entities that compose
the "block definition" at the scale that was inserted
See the attached file, it contain a "block definition" called "pieza"
this definition have 4 lines in layer "lines" and 2 circles in layer
"circles", a "block insert" in layer "block1" and another in "block2".
If you turn off the block "pieza" both inserts are hidden.
If you turn off the layer "block1" the left "insert" is hidden.
If you turn off the layer "block2" the right "insert" is hidden.
If you turn off the layer "lines" the lines that compose the
"block definition" and are in the layer "lines" are hidden.
If you turn off the layer "circles"... you reply and then try ;-)