Visualize Data with a Scatterplot Graph help please

I want to show the ticks on the yAxis every 15 seconds ,I want that to be looked like FCC challenge example

here is my code

also I want to say ,that I get a hard time with time scales ,I find that the d3.js explanation on github is not simplified , it is really complicated , this is my oppinion .

is that because English is not my first language or it is really complicated and needs time to be understood ?

thanks in advance