!rant
Uni homework...

How can I decide if a weighted, undirected graph is connected or not, using Kruskal's algorithm?

It seems you need to run Kruskal's algorithm and afterwards check if all nodes are in the resulting minimal spanning tree.

At least that's what I think after looking at the Wikipedia article about the algorithm.

The problem is - I am a total n00b in graphs. I've never quite got the hang of them...

It's not as complicated as it might seem in the beginning and in some explanations.
Graphs are collections of nodes that can be connected with edges. Weighted graphs have a number associated with every edge.

That's pretty much all there is to it.
Then you need to store the nodes and the edges in fitting data structures.

Thank you guys for the answers - I managed to implement the algorithm in C++. 😃