Advice for using jack stands to hold up a roof?

I am a rookie DIYer. I need to replace some boards on my porch that are caps for my half wall under the porch. It goes caps metal lattice work roof. Do I need jack stands and if I do is it as simple as putting the jacks on a solid surface and jacking them up to the roof so they hold the roof. Sorry if this is confusing but I am a rookie