The built-in sound card on a laptop often ranges between very poor quality to decent, but generally they are not high quality for two reasons: DAC and Latency.
The main issue with laptop sound cards is latency of the interface. For example, a built-in laptop sound card might have a latency of 20-50ms, while an external card made for audio work can have a latency of <10ms or even <5ms.
When an interface has latency, music production might suffer when you are merging different tracks or attempting to match beats DJing etc. <10ms is usually imperceptible, but on high-quality studio soundsystems or PA systems the latency of 20-50ms can start to become noticeable. So, while in your home studio the latency may not be noticeable, once recorded and played on a studio setup you may notice beats and other artifacts to seem slightly off.
A good digital analog converter is expensive, and for this reason laptops and mobile devices are often lacking in quality of their DACs. External sound cards tend to have their own DAC, and these are generally higher in quality than those that ship with the computer. The DAC is important for you listening to music as you create it. If your DAC is of poor quality, you will get a less-than-true rendering of the audio you're creating through your speakers. This can include distortion, noise, delay, jitter, and various forms of digital filtering. So, you may notice that music you create using a built-in laptop DAC sounds different when recorded and replayed through a high-quality DAC.
Also, the nature of the power supply for the audio interface (in the case of a built in laptop, this shares the system's PSU, which is typically not designed ideal for audio and may generate interference and noise as well) and the shielding of the components will be important considerations as well in the quality of an audio interface.
Conclusion: Get a good sound interface, work from there
That said, the addition of a good external sound interface to a laptop can make audio production and performance much better quality. I will echo @RoryAlsop's statements that just having a good CPU, fast SSD and decent amount of RAM should do the trick otherwise for your purposes. As a first step, getting a good sound interface should make the biggest difference and from there you can fine-tune your needs.