"Так" translates to 'so'. Without it, the sentence would be "Я не думаю.", which is just 'I don't think.'
When you heard view and don't agree you can say that " Я так не думаю " and you explain your view or Я ТАК не делаю ..You saw how somebody makes anything, but you make it not so, you will say Я ТАК не делаю
ТАК--it's show that you don't say, don't make or don't think exactly so as anybody speaks, shows. or Anybody talks that you think so and you don't agree "Я так не думаю"
I think so and my mother agrees (her native language is Russian, so), but I think that is only allowed if you want to put the emphasis on the word ‘так’.
Whenever you want to know the infinitive, or the other conjugations for a verb, you can check one of these two links below, where you can find a verb searching for any of its conjugations or forms.
http://cooljugator.com/ru/ (in this site you can also search for the verb in English)
http://starling.rinet.ru/morph.htm (click in "English" to change the language interface, and be aware that this site unfortunately doesn't recognize the letter ё, so you should replace it for е before searching for a verb that contains it)
In Russian, it means along the lines of ‘so’, ‘like that’, ‘in that manner’; just like the English translation suggests. In Ukrainian, it means ‘yes.’