How to make video calls on my laptop? pls see the details........?

iam neewly purchased a Dell inspiron. and my sister is in UK when i connect them to make a video call, my sister said ur in off idont know what to do? will u please tell me the how can make avideo call? and can i install any softwares ? and how to instll softwares through net? my datacable is Reliance from india.