I just created a map.Its several land with an island.How can I connect the island to one of the land?

If you mean making the mainland and an island into one territory, there is an option in Inkscape called Path -> Connect. Select two paths by shift-clicking them and use Connect, and it will become *"one path"*. Then lable it Territory_112 *(just an example)* and it's one territory.

If you mean making a connection between an island and the rest of the map, so that you can attack *(from)* the island, you can just make a connection in the Design Map Editing Screen as you would connect any two other territories.
It is recommended that you make a line *(usually yellow)* in Inkscape between these two territories *(before uploading it, of course)*, so that players can see the connection.
You needn't lable this line, since it has no gameplay function.