The boxes get small at 4 and 5 generations, that's normal for this chart. Plenty of people print the 3-generation version once for each grandparent's line instead of one crowded sheet.
How to fill it in
Start with yourself in the bottom box, then work backward. Each row above holds one generation further back: your parents, then your grandparents, then great-grandparents if you picked 4 or 5 generations. In every pair, the box on the left is the father's side and the box on the right is the mother's side, so the same pattern repeats all the way up the chart.
It's fine to leave boxes blank. A template like this is meant to be built up over time, and a few conversations with relatives usually fill in more than you'd expect. If two people share a box (for example, a grandparent you never met), write what you do know, even just a surname or a place, and come back to it later.
Why the rows double
Everyone has exactly two parents, so the number of ancestors doubles every generation back: 2 parents, 4 grandparents, 8 great-grandparents, 16 second great-grandparents. Genealogists call this doubling layout a pedigree chart, or an ahnentafel (German for "ancestor table"). It's the standard shape for this kind of chart, which is why the boxes get narrower the further back you go. The great-grandparent row and the row above it are labeled GGF and GGM (great-grandfather, great-grandmother) and 2xGGF and 2xGGM (second great-grandfather, second great-grandmother), short forms genealogists use, so the label fits the box.
A pedigree chart like this only has room for one direct line, no siblings, no partners, no photos. Once you want the whole family together, not just your ancestors, Family Tree Studio builds that on a canvas and turns it into a print-ready poster. If you'd rather look up exactly what to call a relative once you've mapped them, the cousin calculator and the relationship chart cover that. And if you already have a tree in a GEDCOM (.ged) file from another program, the GEDCOM viewer lets you browse it right in your browser before you fill anything in by hand.