How to tell if stripboard is plated or not?
If the copper looks copper coloured it’s almost certainly not plated. Plating would probably be Tin (silver colour), or possibly Gold (gold colour). When copper corrodes it produces Verdigris (bluish-green colour). If this is the case a quick rub with wire wool / fine sandpaper / any mild abrasive will clean it off. Your board looks good to use as it is. You should be using solder for electronic components, which has flux within (often called multicore) the flux chemically cleans both the board and the component to allow a good electrical (and to a lesser degree mechanical) joint when melted by the soldering process.

Hope this helps, and good luck with your project.