Singed is in my opinion one of the most versatile champion, Farming, Team fights, Pushing. The whole 9 yards. In this guide you will learn how to play Singed as a tank. His innate (25%) of his mana is converted to health. Makes Singed able to get a lot of mana and at the same time health.

You want to push this item first (getting it early allows for stacks early-mid games.)
When a Rod of Ages has reached maximum benefits, it grants the following:
630 HP
725 Mana (+181 health)
80 AP
Faster movement more poison spread self explanatory
This helps to boost AP and helps greatly with health
Total mana add: 1400 (+350 health)
Just a good health boost to make you really tanky.
Whats 5k health without regen?
You have now become the flinging wonder. Not only does your poison and fling slow. But your slow slows (Who would've thought).

Help to run and to catch up if your ult is down. And it allows you to Fling/harass a low health enemy while going through their minion waves. (very effective with poison.)
This will save your life with many lulz to go along with it. Simply fling and fortify and slow an enemy and just watch as your tower does the work!

Pros

Very good creep farmer
Very good initiator
Good in team fights and getting your allies that kill/save that earns you a proper Thank You.
Enemys cant just ignore you like your a big meat balloon (Cho'Gath)

Cons

Kind of slow until you get your tanky items.
Your poison is slow until late mid-late game.

Fling makes Singed an incredible team fighter and initiator. Basically you want to Ult, Poison, Fling, and slow. Then when your enemies try to run simply fling again. If you do this right, Towards the end of the game people should be ranting about how Fling is OP.

Singed can be one of those champions that people play with and they pray that he knows what he's doing. And theres nothing more satisfying than flinging someone into your kill hungry team, and watching them being devoured. a few helpful tips with singed. Do not tower dive early game. Do not rush in like your superman. Thanks

PS: I normally get more assists than kills as singed normally a 2/1/4 ratio.