There are different ways to define a block statement.

Name

You can select by block name. Make sure to include the entire name, also the namespace. For example if you want to state a grass block, you do minecraft:grass_block.

Tag

Select by tag is also an option. Simply add # in front of the name (the same formatting as vanilla tags). Example: #minecraft:logs will include all blocks which are part of the logs blocktag.

Property

Furthermore properties can be defined. Example #minecraft:leaves[persistent=false]. This will only include blocks which have the given property and the exact defined value. So the example will only include blocks which have the property persistent and the value false for it. All other blocks will be left out. You can define multiple properties by separating them with a comma.

Retrieve information about a block

Using F3 ingame is a good way to get all the needed information of a block:

color	purpose
yellow	exact block name
red	properties
blue	tags