My question is how to sing it?Yes. This is not a simple book, but thatæ's why it's good.
You don't want to rush through it. You want to play it well and also do the singing. It's about quality. This is how the Dave's and the Vinnies learned to play so clean.
If you haven't done ostinato with reading exercises before you should probably folllow the order, you should probably do that anyway, but if you think it's easy at first, relax, it gets harder. Much harder. There's a second book, as well.
Also, there's no rule saying you can't make your own ostinatos. As mentioned, people have done this for ages. These guys just started organizing it into method books. You don't get the teacher with the book though and from what I've heard they were all about the music and groove. It don't mean a thing......
Is it bad if I counted until now for example;

1, 2 &, 3 e & a, 4 ? i'm counting and including the melody and humming it like a song.. or I've to stick with quarter notes?
and what do you mean about articulation?

1 e a , 2 & a , e & , 4 e & a - is that the right counting?
just a week ago I've started to learn reading so I just wanna be sure
thank you so much