If I understand your goal (unassisted speech to text conversion, using Praat), this is not doable out of the box, but you might eventually develop the tools for doing this. An alternative interpretation is simply "how do I find phonetic landmarks, using Praat and my ears?", which is actually quite doable, if you know basic phonetics.
Before you get to using Praat, you need to decide what the scope of your project is: any language, or a specific language? If you can't do it for a specific language (and then for 6 specific languages), you can't do it for all languages. If you know what the language is, then you can use that information to rule out possible interpretations of the signal. Within Praat, you have basically two problems, segmentation and identification (the latter assumes the former). The easiest case for segmentation in picking segments in a VCV sequence with voiceless stops, then fricatives, then voices stops, voiced fricatives, nasals, laterals, rhotics and glides. The reason why VtV is easiest is because a big change in the signal matches segment boundaries. The endpoint of the process is parsing similar vowel sequences such as [eɛ, ɨi], where it's impossible to find a crisp segment boundary (and the usual approach is to divide the contested zone in two parts).