The three main things that will dictate the performance of your laptop are the CPU, the GPU, and the HDD/SDD. Ram plays a part in computer performance but isn't as dire as the prior. For a good, solid gaming laptop I would recommend getting at least 8gb of Ram.
A good will affect the system as a whole your Pc's speeds will vary greatly depending on te processor you choose.
A good GPU is only crucial for any gaming PC. You can build or buy a PC with the best specs in the world but if you go and put a cheap GPU in it you can forget about gaming. What GPU you choose for your laptop depends on what sort of gaming you plan to do on it.
Your HDD/SSD will change your boot time, read/write time (time to write to the drive and time to read it, better times result in faster downloads and quicker launches of applications. In some cases better drives affect fame performance too). I strongly recommend getting an SSD while they do cost more than an HDD they are much quicker and are even capable of reviving and old machine because of their speed.