If you're looking for an easy way to get an infinite amount of the same element, you need the CLNE/BCLN (breakable CLNE variant)/PCLN (switchable CLNE variant)/PBCN (destructible PCLN variant) element. Place one pixel of any of these (CLNE will probably be best for your purposes) when simulation is paused, then click on it after selecting the element you want to clone first, and CLNE will create that element indefinitely.