Understanding the use of the keyword every

My question regards the keyword every that is used to sample an input data file (i.e., .csv, .dat etc.). I am reading the documentation of the keyword that says the following:

     plot 'file' every {<point_incr>}
                         {:{<block_incr>}
                           {:{<start_point>}
                             {:{<start_block>}
                               {:{<end_point>}
                                 {:<end_block>}}}}}

The thing is I cannot completely comprehend how to adapt this to a data set. For instance, if I have some dummy data that I wish to use to create a bar chart for example and the data are the following

# first bars group
#x axis   #y axis
0          2
0.2        3                  
0.4        4                  
0.6        5                 
0.8        6                 
                             
#second bars group           
1          1 
1.2        2
1.4        3
1.6        4
1.8        5

#etc.
3     10
3.2   20
3.4   30
3.6   40
3.8   50 

4     20
4.2   30
4.4   40
4.6   50
4.8   60 

And lets say that I want to create four bar clusters from the data. One for every block. How can I use the syntax of the keyword? Could someone give me some examples to better understand the use of it? Thank you in advance

As you've found, the every keyword allows you to cherry-pick a subset of single-newline-separated points and double-newline-separated blocks from your datafile. Your example datafile shows 20 points divided into 4 blocks.

So to plot the first block (indexed 0 in gnuplot), you only need to specify the end block, and use the default values for the other every parameters. Try:

plot 'data.txt' every :::::0 with boxes

It seems your goal is to plot each block with separate styling. Here's how you could do that with a few extra styling commands. (Note my use of gnuplot's shorthand for some keywords.)

set key left top
set boxwidth 0.2
p 'data.txt' ev :::0::0 w boxes t 'first',\
  'data.txt' ev :::1::1 w boxes t 'second',\
  'data.txt' ev :::2::2 w boxes t 'third',\
  'data.txt' ev :::3::3 w boxes t 'fourth'