First, select the vertices as shown on the next picture:

Then, move them, in the front view, into the position ass seen in the picture.

Select the polygons from the picture and extrude them a little.

At the moment we have too many polygons where we will attach the wind to the body, so we need to tidy that up by target welding the vertices.

Create a box with 4 segments in the top view and convert it to editable poly.

Move the vertices so they follow the shape of the wing.

Select all the wing polygons and by using Slice Plane tool cut it in the middle.

Next, adjust the wing vertices in the front view.

Select the body of the airplane, go to the Edit Poly options and select Attach. Click on the wing. Go into the Polygon Select mode and select polygons on the wing and the body as shown in the picture.

Click on the Bridge button, while the polygons are still selected, to “bridge” the wing with the body.