This is a mould to make silicone pads that can be stuck onto the underside of objects to prevent them from sliding around on surfaces.
Put a thin layer of petroleum jelly (aka Vaseline) on the surfaces that come into contact with the silicone. Dispense DIY silicone sealant into the mould and smooth flat with a filling knife/spatula (a print bed scraper works very well). Leave overnight to set, then separate the two halves of the mould to remove the silicone pads.
Clean the pads with isopropyl alcohol and stick in position with a blob of the same silicone sealant.