I found this awesome site that told me how.
i am baker
I didn't have the right tip, it's on my "to buy" list now, but I gave it a go anyway.
Tomorrow is my mother-in-law's birthday so I made a strawberry cake with buttercream icing.
Not too bad for a first try and with the wrong tip.
Okay, it looks nothing like hers and it slightly resembles roses but I think it looks beautiful.
A+ for effort.