Simple enough, you just need to place a workbench on each of the main islands in the first 3 areas. Ther are 10 islands in area 1 and 15 in each of areas 2 and 3. None of the vacant islands need to be done, and the workbench does not need to be upgraded of used in any way.
Others have suggested that you need to place and additional workbench on the first island (as you repair one as part of the tutroial) but I can't confirm that.
In the spoiler below is a list of all of the islands for those that want it to check them off as you go.
*** Spoiler - click to reveal ***1-01 - Squire's Knoll
1-02 - Dusty Junction
1-03 - Fort Finch
1-04 - Shrieking Sands
1-05 - Garnet Peaks
1-06 - Autumn Springs
1-07 - Port of Caul
1-08 - Orson Orchards
1-09 - Callum's Claim
1-10 - Plains of Passage
2-01 - Landlubber's Leap
2-02 - Brackenburg
2-03 - Hintertown
2-04 - Witchwater
2-05 - Joren's Outpost
2-06 - Angler's Wharf
2-07 - North Point
2-08 - Ghostlight Mire
2-09 - Mosakola Harbor
2-10 - Addermoor
2-11 - Broadside Bay
2-12 - Mount Meridian
2-13 - Mayyan Delta
2-14 - Deepest Mosakola
2-15 - Morello Marshes
3-01 - The Great Scar
3-02 - Pockmark Plains
3-03 - Facetta
3-04 - Glimmerglen
3-05 - Lunar Landing
3-06 - Sea of Stalks
3-07 - Farpoint
3-08 - Filia's Folly
3-09 - New Caul
3-10 - Pillars of Parun
3-11 - The Bone Wastes
3-12 - Starspires
3-13 - The Motherlode
3-14 - Old Hintertown
3-15 - Great Frontier