Is there any principle difference between "ρόδα" and "τρόχος"? Thanks in advice))
No, it's the same (careful with the accent placement, it's "τροχός"). It's just that, depending on the phrase, sometimes only one of the two is used: "the invention of the wheel" is always "η ανακάλυψη του τροχού". "Pόδα" is probably a bit more frequently used in everyday speech, as if you use "τροχός" for bikes and cars it sounds a bit old-fashioned in comparison, but otherwise they are both very common, depending on the phrase as I mentioned above.
απηντησα :χρειαζομαι ενα τροχο,ΠΟΥ ΕΙΝΑΙ ΤΟ ΛΑΘΟΣ; ΠΑΡΑΚΑΛΩ ΘΕΛΩ ΠΙΣΩ ΤΟΥΣ ΠΟΝΤΟΥΣ ΜΟΥ ,ΔΕΔΟΜΕΝΟΥ ΟΤΙ ΕΙΝΑΙ ΣΩΣΤΗ Η ΑΠΑΝΤΗΣΗ ΚΑΙ ΜΗ ΜΟΥ ΠΕΙΤΕ ΓΙΑ SCREENSHOTS ΔΕΝ ΓΝΩΡΙΖΩ ΝΑ ΣΤΕΙΛΩ