is it possible to let's say (just an example) buy 5000 shares @ 17.56, and sell them a few secs later @ 17.57?
Yes, it's possible. But what if a few seconds later it's at 17.46? Now you're down $500. What do you do? Do you hold on and wait for it to come back so you can break even? While you're waiting, it drops to 17.36 and you're down $1000. Now your palms are sweating and your head is spinning because you really can't afford to lose that much. When it drops another 10 cents, the pain becomes unbearable and you sell. 10 minutes later it's at 17.77 and you feel like kicking yourself, so the next time you hold on a little longer, but lose again. Then you bet a larger amount than usual because you need to recoup your losses. That doesn't work out and now you're broke and a statistic.
There's a reason why this is one of the hardest professions to succeed at. Read several books and spend some time on these boards before putting real money to work, and then in small amounts until you are consistently profitable.