To ‘go long’ on something, is to pay for it now in the hope that it will go up in value – as opposed to going short which is to sell something now and pay later for it, hoping that it will have lost value in the meantime.
By making any investment in the hope that it will increase in value, you are ‘going long’ on an asset. If you buy gold now and it goes up in value over the next 10 years you have profited by holding it for a long time and benefitting from a rise in price when you come to sell it.
By finding and holding an asset that has increased in value you can protect your wealth because you are not exposed to inflation. Assets such as gold tend to go up, thereby increasing their value in pounds.