<font face="Verdana, Arial, Helvetica, sans-serif" size="2">How long does it take to give blood? How painful is it?</font>
Analise,
It feels much like a regular injection. The only painful part is when the needle punctures your skin. You might then feel slightly uneasy while the blood is extracted (for a minute or so?), but this is mostly psychological.
Remember to eat well and not exercise strenuously afterwards.