Hi Guest you really need to join GoY and give us more info on your planned project

Very briefly, firstly clear the area of whatever is in it now, and level the ground.

Cover the area with a membrane which lets water through but not weeds - you can normally get this membrane/fabric at any garden centre.

Next choose what type/colour/ particle size of gravel you want, get it delivered and lay it over the membrane. The bags of gravel will normaly tell you on them what area they will cover. Builders merchants may have gravel, DIY stores have it and so go most garden centres.