The fundimental job of a soundcard is to convert audio signals into data while recording, and then to convert data into audio signals for playback. This called A/D (analog to digital) and D/A (digital to analog) conversion. No matter how much money you throw into your computer in the fastest CPU, most expensive RAM, yadda yadda.... the soundcard determines how good your computer sounds. As mentioned, it also determines how many tracks you can record at once, with most built in soundcards only allowing 1 stereo, or two mono tracks at a time. If that's all you need for now, then it's a question of whether the quality is good enough for now. A secondary function of the soundcard is to provide preamplification for a mic level signal. Most computer soundcards, or on board sound chips, provide a line level and a mic level input jack. The soundcard may do a decent job with line level signals, but may have a terrible mic preamp. If that's the case, and it often is, then you may get decent results by buying an external mic preamp, and connecting it to the soundcard's line input jack.
Eventually, if you get into this recording endevour, you will want to upgrade to a better interface with more I/O, and better sound. You just have to first evaluate if what you have is usable, and then what your purchase priorities are.