"I am standing by the table."
Translation:Stoję przy stole.
For the meaning: in this case (and in most cases) it is almost the same. For spatial relations, "przy" may be understand as closer (side by side, touching or almost touching one another) than "obok", which may imply some short distance. But this is nothing you should care about up to about B2 level.
For the grammar:
"przy" is used with noun/adjecttive/numeral in Locative Case: przy stole, przy mamie, przy drzewie, przy samochodzie.
"obok" with noun/etc in Genitive Case: obok stołu, obok mamy, obok drzewa, obok samochodu.
Thank you and immery below for the differences.
However, I would wish people stop replying with "you don't need to know this now." It is best to have the proper roots when able before one gets too comfortable using the wrong thing and therefore it is much harder to change later. Especially in the cases where someone asks directly, clearly for the purpose for understanding the difference. (It is fine that we are not tested on the distinct difference yet, though.)
Obok is literally side by side. The wardrobe is obok bookcase, but przy wall. But mostly it is set expressions and personal preference.
siedzę przy stole is when I sit in a usual position to eat or work at the table, siedzę obok stołu is when I sit and have a table at my side instead in front of me.
Why can't I say "Jestem stoję przy stole"? Is "jestem" redundant in this case or is not the right context to use it?
It's just wrong. Don't think of the Present Continous construction (I am -ing) as anything else than a construction. There isn't really any 'to be' there. You only translate the verb.
And, especially that in 99% of the cases Polish translates Present Continous and Present Simple the same way, your sentence is like "I am I stand at the table".
Emm because in Polish language this is doesn't have meaning. You must say ,,Stoję przy stole". I'am-Jestem.
As a general rule, you should forget about translating prepositions literally, because they work in Polish differently than in English. In my opinion it is better to learn them by expressions or verbs that they are used with.
Having said that, "in front of" means rather "przed" (as "before") than "przy". E.g.: "I stand before an important decision" - "stoję przed ważną decyzją" or in front of a building "przed budynkiem".
If we say "ja stoję przy ..." it rather means that I stand "by the side of it" than in front of it. If we say "ja siedzę przy ..." then, depending on context it may mean e.g. "siedzę przy chorej żonie" I am sitting by my ill wife - or "siedzę przy stole" - I am sitting at the table.