Ruvox and maximus43 are correct! To sum everything up the following scenarios are possible:
A resource appeared on your land, but you are physically located elsewhere (i.e. outside of its circle).
You can either travel into that land's circle and use "Capture" (round flag button) anywhere on its territory (the land will upgrade to the next level, grow a little bit and collect every resource located there) or move closer to the resource itself and use "Pick up" (round button with a hand) to directly interact with a nearby resource.
Alternatively, you can build a Tracking Satellite and collect resources remotely, as mentioned by Ruvox.
If the resource did appear on a land where you're standing and "Capture" button still doesn't pick it up, perhaps the resource is located slightly outside of the land's border?
I'd zoom in really close to verify its exact position.
If that is the case, then upgrading the land a few times will eventually reach and collect the resource.
However, if this land is a base you will need to capture more lands outside of it for that land to grow (sometimes it's easier to just approach the resource directly and pick it up manually using the "hand" button ).
Once you acquire some resources the first building I'd recommend constructing is the "Assembly Plant" - it allows producing tools that extend your resource collection radius and make life a lot easier!
I hope that helps, but if not - perhaps you could upload a screenshot showing the problematic resource, so that we could better understand your scenario?