The Number block outputs a given value.
To change the value of the number block, select the block, then tap the button right below the open inventory button, in the bottom right corner.
This will open up the keypad, which you can use to change the value that the number script block will output.
The number is the most common data type. Numbers are represented by blue wires.
Numbers are stored as 32-bit floats. This gives numbers a maximum value of 340,282,346,638,528,859,811,704,183,484,516,925,440. Likewise, their minimum value is the negative of that.
Numbers have about 7 digits of precision. This means that numbers with 8 digits or more may begin to give slightly inaccurate results, e.g. when adding numbers together. The margin of error is usually tiny, but gets larger the more digits you have.