925 Silver - (or sterling silver) is 92.5% silver with the remaining 7.5% an non silver metal (usually copper). Jewellery made of 925 silver will generally be a lot more durable, less likely to tarnish and be of better quality.
Silver plated - Silver plate is a thin layer of real silver that has been plated onto a cheaper metal alloy. The under metal is usually a nickel, brass or coin silver, but it can be any kind of metal.
Tibetan Silver/Nickel Silver/German Silver - these names are generally given to an alloy that looks like silver but normally contains a mixture of metals (none being silver). These alloys can usually be made of tin, zinc and copper (and other metals). Please do not purchase these if you are looking to buy genuine silver.
Silver tone -Silvertone is simply metal or plastic made or coloured to look like real silver. It may be metal and it may be a silver color but it is not sterling silver. In fact, silvertone is not a metal at all. Silvertone is more a reference to colour and sheen.
As with all jewellery - do not wear when applying skin care products or perfume