Lead free solder was developed to comply to the European Union Waste Electrical and Electronic Equipment Directive (WEEE) and Restriction of Hazardous Substances Directive (RoHS), prohibiting the inclusion of significant quantities of lead in most consumer electronics produced in the EU.
The main difference between the lead and lead free solder is the temperature it takes to melt the solder. Lead free solder has a higher melting point then the tin/lead solder. The down side to lead free solder is that it is more likely to have solder bridges (shorts) and is more likely to have tin whiskers form.
But the best thing to do is practice with both just to make sure you have the hang of it.