The summoner under the College of Winterhold

That is the Atronach Forge. You can use it to create various Atronach related items such as spell books, staves and scrolls by placing materials in the donation box and pulling the lever.

You can also use it to create Daedra Armor and Weapons using a Sigil Stone. You will need 90 conjuration to get this stone.

http://elderscrolls.wikia.com/wiki/Atronach_Forge

The game can be played any way you want, but some of the advantages of visiting the College of Winterhold are:

• Access to spells: spells from all schools of magic can be bought there
• Mage-friendly quest rewards: you'll get quite a few nice mage-centered quest rewards, like the Archmage robes and the Morokei mask
• Access to trainers: if you feel like paying for training, the high level mage trainers are mostly (all?) in the College of Winterhold

It is a long way, but you can easily travel there using a wagon. If you're following the main quest line, once you get to Whiterun you can take a wagon from in front of the stables.

So, I would recommend traveling there shortly after you reach Whiterun. After getting Lydia or after visiting the Throat of the World seem like good times to peel off and do the mage quests.