Quote Originally Posted by LArdius View Post
Manual as in the booklet manual. There are two buttons beside each other, the one on the left is the one which enables me to flash fire.
Please read again your manual (thoroughly) and also please describe clearly which button you are pressing and also which camera you are using. It helps a lot since the art of mind reading is not very common.
In case you have a Canon camera then spheredome has given you the answer, the respective chapter in the manual is label "FE lock" (e.g. for 450D on page 89). Since it's just a brief burst with reduced power you can repeat the function faster.
Second curtain flash can be set in Custom Functions. For firing a flash somewhere in between during any bulb exposure you will need an external flash. That's beyond the scope of the onboard flash.