Get blocks in the inventory?

I'm still new to Minecraft and I just can't get blocks into my inventory.

How do you get blocks into your inventory, because if I just hold down the left mouse button for a long time, the block is gone…

Do you mean from a box or something? Thanks left click and drag over. Or Shift left click then a stack must go directly into your inventory. You can pick up blocks that are on the floor without doing anything.

If you hold down the left mouse button, you dismantle the block.

You can break down certain blocks by hand, it takes a long time for them to "break" and then they are simply gone.

You can use your hand to mine wood or earth, for example, which is then dropped and ends up in your inventory.

I have something for you when you're just starting out with Minecraft!