Differences between Fe3+ and Fe2+
The only thing that's different about ${Fe^2}^+$ and ${Fe^3}^+$ is the number of electrons, which in turn results in different properties of these species. 

${Fe^2}^+$, aka ferrous, is pale green and turns violet when added to water. ${Fe^3}^+$, aka ferric, is yellow-brown in solution. You can use several methods to distinguish these two ions. I will mention some of them.

${Fe^2}^+$ can oxidised to ${Fe^3}^+$ with the help of oxidizing agents like $KMnO_4,\space HNO_3$, etc.. $KMnO_4$ is better because its pink color decolorizes on addition of ferrous ions.

Another method to distinguish them is by using colored complexes. For eg., ${Fe^2}^+$ forms a red-orange compound with amine lignads. ${Fe^3}^+$ forms blood red solution with thiocyanate ions, which is used as fake blood in movies, dramas and so on.

Ferrous ions normally have paramagnetic properties, but can become diamagnetic due to the formation of low-spin complexes. A ferric ion is only paramagnetic due to the presence of only one lone electron.