R is how many cases one person infects. It's connected to how quickly the virus doubles. However, when you're working it out, you also have to know what period of time someone is contagious for.
Imagine for a fictitious disease, it had an R of 10 (very high) but had a year long incubation period before the person was infected. Then you might have a different disease, which only has an R of 1.1, but carriers are infectious immediately and only for a single day. The second virus has a lower R, but will grow much more quickly.
With Covid, we can just about see how quickly it's growing, and we know more or less what period of time someone is contagious for. From these two things, we can work backwards to give a rough estimate of what R is. It's always going to be an estimate, because we don't know precisely when people are most contagious and we also don't know exactly how many people have it, or how quickly it's growing.
The rate of growth is just as important as the R value and more comprehendible. Back at the beginning of this pandemic, cases were doubling every 2-3 days. Currently, cases are halving every 2 months. It's a lot quicker on the way up than it is on the way down, which is why it's really, really important not to let cases rise again after you've fought tooth and nail to get them down.