Wa aleykum salam.
The difference between shia and sunni is which hadiths we believe in (in the hadiths on how the Prophet (saw) died, who his successor is, how he used to pray, sayings on different subjects..)

Shia Muslims are followers of Imam Ali  (as) because we (shia) believe in the ahadith where the Prophet (saw) clearly acknowledge Imam Ali (as) as his successor. Ahlulbayt (the family of Prophet Muhammads s.a.w. family) has a major role in Shia Islam according to this hadith. Hadith al thaqalayn:

I am leaving among you two weighty things: the one being the Book of Allah in which there is right guidance and light, so hold fast to the Book of Allah and adhere to it. He exhorted (us) (to hold fast) to the Book of Allah and then said: The second are the members of my household I remind you (of your duties) to the members of my family.

This hadith is accepted by both sunnis and shias. But the two groups differ on the exact wording of what the Prophet (saw) said.
Shias believe they follow the Prophets (saw) sunna, while Sunni Muslims believe they follow the real sunna. You see, this is a complicated subject and I can write about this for hours.

There are a lot of misconceptions about shia. Like let’s say, that we pray to a stone. When in fact, we pray on it (it’s called turbah, and it’s mud from Karbala) because the Prophet (saw) used to make sujod on mud. You (not personally you, but sunni muslims in general) say that we worship this “stone”, but when you make sujod on your rug, does that mean you are worshiping the rug? Of course not. 

We have difference of opinion regarding hadiths and tafseer of the Holy Quran.  But we are all Muslims alhamdulillah, and that’s what’s important. I think it’s kind of sad when someone tries to correct you on the shia/sunni issue, when that person is full with flaws him/herself. We should focus on praying on time, praying correctly and light our own candle before we even try to light someone elses candle.  I maybe sound like a hypocrite now haha, but I just answered your questions. :) And please, correct me if I said anything wrong.

Jazak Allah Khair.