Hi Vedry A good question! I found a page which explains this quite well: http://www.englishpage.com/minitutorials/also.html

we used "too" when trying to exprese something or filling eg. "i am very happy with you," than you can also said "i am happy with you too" it means you have the same fillng with him. "also" doing something very similar. eg. "i was at the filed yesterday" you can reply " i am also at the filed yesterday".