complete the eoc tutorial north of lumbridge (15 minutes it should take) and then after you've finished, right click start training on lady deathknell (the tutorial person) and it will open up an interface like this, just click on each square under 'ranks earned' and you'll be given an xp reward book that you can use on any combat skill (including slayer + summoning), there's 21 total that you can get!
at level 99 i received 9,703xp = 203,763xp total!
edit: you can teleport directly there by clicking the tab next to the inventory which has a question mark on it and clicking 'go to academy'