Some use ponchos.
Some use rain pants, rain jacket and backpack cover.
Some use rain kilts instead of rain pants.
Some use umbrellas.
Some use poncho-like raincoats that also cover your pack, like the
Altus poncho.
Some use flimsy single use ponchos.
Some just cut holes for head and arms in a large trash bag (yes, actually saw that).
Some don't bring any rain gear at all in summer, and just hope for the best (not a wise choice... especially on mountains...).
It all depends on personal preferences and the time of year you're walking. My advice would be to go for some long walks in the rain with the equipment you already own and see how well it goes. If it doesn't work for you, try something else. There are many options to choose from, so you'll certainly find something you feel comfortable with
Poncho or rain jacket/pants are both very popular and good choices for walking the Francés in april/may.
Happy planning and buen camino!