This is a broad question. If you were more specific, I could give a more specific answer. Generally speaking a resource is anything that a person, group or nation has to use. Perhaps some examples will be best.
If a nation is said to be rich in natural resources, then that nation has things like oil, zinc, copper, agricultural products, and other things to support life, trade and prosperity. In this regard, Saudi Arabia would be rich in resources when it comes to oil. America would be rich in terms of corn, and China would be rich in terms of rare earth elements.
If a person is said to have financial resources, then it would mean that a person has money to spend, invest, or use for other purposes.
From these examples, we can broaden things out a bit and speak of resources in knowledge, power, and connections (as examples).