Select the shape according to width of gap or joint to be coverd.
Then, please ensure gap is clean and no obsturctions, because they would prevent shape from remaining level on tiles or flooring materials.
Using silicone or elastomeric to caulk the gap, one thing need to pay attention, must being careful not to overfill.
Insert the anchor leg into gap so that the edge of profile rests against the edge of the flooring material and covers the gap. The anchor leg should be partially buried in the sealant. Softly moving profile, makes it straight.