Check all parts are present - you should have
5 x pillars
4 x retaining wall wings
2 x end walls
5 x small pillar locating parts
1 x bed deck
1 x steel girder under deck
Identify the top of the pillars. You will see a small rectangle on the top of the pillar. This rectangle fits into the pillar locating parts. Some minor sanding/filing may be required to fit the two parts together. Once a suitable fit has been achieved glue. Identify the end walls. The end walls have a pair of columns on each wall that accommodates the track bed. Fit a pillar into the rebate of the end wall and glue. Use the shallowest rebated side of the end wall to accommodate the pillar. Fit together and glue. The columns of the end wall require the retaining wall wings to be attached. Centre the retaining wall adjacent to the column and when satisfied glue.
Paint the assembly of the end walls and retaining wings. Paint the remaining pillars. Paint the deck and paint the girder under deck.
Once the paint is dry glue the deck and the girder under deck. Make sure the flat sides are glued together. The two parts must be symmetrical, take care to centre the girder onto the deck. The girder must have the rebate visible this accommodates the locating part with the pillars. It helps centre and square the pillars. The deck must have the small wall upper most to retain track ballast.
Position the pillars with their locating part on the girder and deck assembly. Set the pillars in the position you desire. They are usually at even distances apart. Once satisfied glued.
Weather and attach to layout.