Hi,
You should first import just the basic the products. For example T-shirt, Sweater. Then create the combinations for them. If your T-Shirt's id is 1. And you have it in black and red and in sizes S, M, L, your combinations CSV should look something like this:
Product ID;Attribute;Value
1;Color:color:1,Size:select:1;Black:1,S:1;
1;Color:color:1,Size:select:2;Black:1,M:2;
1;Color:color:1,Size:select:3;Black:1,L:3;
1;Color:color:2,Size:select:1;Red:2,S:1;
1;Color:color:2,Size:select:2;Red:2,M:2;
1;Color:color:2,Size:select:3;Red:2,L:3;