Summoning in Prothieum is a rather hard skill to train but is required to achieve maximum combat level and to be able to summon helpful familiars like War-Tortoise and Pak-Yak.
Summoning also requires a cash stack of around 25m because buying the shards are very costly, being 100gp per shard in G.E. And in which some pouches require up to and over 100 shards PER pouch. Which can make higher level pouches cost around 10,000gp each, and making a full inventory can cost you up to 270k per inventory!
Lower levels are very easy. You can make any pouch and you can get up to level 65 very easily, within 5 minutes.
Now, at a higher level (atleast 63), make Evil Turnip pouches. These require 1 evil turnip, 1 crimson charm, and 104 spirit shards. Look below for how to get the ingredients!
How to make Evil Turnip Pouches:
Evil turnips are easy to obtain as they are in the G.E and are very cheap. Go ahead and buy a whole bunch :D
Charms are easy to obtain from any monster. Crimson charms specifically are dropped by Crawling Hands and they drop them more frequently than any other charm, and usually dropping 30-60 at once. Killing Crawling Hands are not hard of course, because they are level 12 and below.
Spirit shards are costly but are easy to obtain. Go ahead and buy them fron the Grand Exchange. If you need help with money, Jadinko's drop cash stacks every time with up to 500k per drop! Go to the Jadinko lair at ::jadinko for some quick cash! Be careful though as they can, yet not often, hit up to 250 and more, so I wouldn't recommend AFK'ing them.
Now time to get that skillcape:
Now that you have all the ingredients, go and make the pouches! The obelisk is right at home. This will take some time and money, but be patient. Best of luck!