There is another character Think - 思 (Post 154), I will discuss the difference between the two characters in the end of this post.
The big seal script of character Think is
The small seal script of character Think is
Similar to big seal script, the top is character Mutual - 相， the bottom is character Heart - 心。
The clerical script of the character Think is
The top is Mutual - 相，the bottom is Heart.
The pinyin of the character is Xiang3.
The character 想 is exchangeable with 思, sometimes people just put them together to form a word 思想, which means Think too. But from the original pictography, there is subtle difference between the two.
思 is more likely internal thinking, 想 is more likely external thinking, that is to watch something, then think. 思 may be more focus on abstract problems, more difficult, like math problems; 想 could be much wider, and easier problems, like to think if I should learn Chinese. 思 may involve more emotional feelings, 想 could be just Desire or Want some foods, or physical objects.
Anyway, they are very close, most Chinese have never thought what the difference of the two.