Will the screen size be of a phone? i want it to be the size of my laptop screen?

Yes, it can be shown as a phone or with a custom resolution. In Display > Primary Display, a predefined resolution can be chosen or a custom one defined, and a skin such as phone-1 or phone-2 can also be used to give it a mobile appearance. Virtual Devices Settings, How to create your own skin in Genymotion Desktop?

To make it fill the laptop screen, Full screen can be activated or the window adjusted to fit the content. Basic Controls