Selection Sort:
Given a list, take the current element and exchange it with the smallest element on the right hand side of the current element. 
Insertion Sort:
Given a list, take the current element and insert it at the appropriate position of the list, adjusting the list every time you insert. It is similar to arranging the cards in a Card game. 
Time Complexity of selection sort is always n(n - 1)/2n(n - 1)/2, whereas insertion sort has better time complexity as its worst case complexity is n(n - 1)/2n(n - 1)/2. Generally it will take lesser or equal comparisons then n(n - 1)/2n(n - 1)/2.
Source: http://cheetahonfire.blogspot.com/2009/05/selection-sort-vs-insertion-sort.html