偏光板の時は、まず偏光板をつけ上に保護板（透明アクリル板）をつけセットします。

、（）。

For the polarizing plate, first attach the polarizing plate, then place the protective plate (transparent acrylic plate) on top and set it in place.

Literal

Polarizing-plate [possessive-の] time [topic-は], first polarizing-plate [object-を] attaching above [to-に] protective-plate (transparent acrylic plate) [object-を] attaching set.

Technical assembly instructions. 偏光板 ('polarizing plate') is optics vocabulary. まず ('first') sequences the steps. ~をつけ is the connective form of つける ('to attach'), chaining two actions. セットします is the loanword する compound. Parenthetical (透明アクリル板) clarifies the technical term with a description. Dry, procedural language.