A fixed asset is something a company has a long period of time to pay for such as a company car. The depreciation side is really simple, if a car cost £10,000 and the depreciation was 10% for 5 years then that means that;
10% of £10,000 = £1,000
£1,000 x 5 Years = £5,000
At the end of these five years the car is worth £5,000 and your fixed asset is paid off.