If we are talking about something similar to the P-spot beads, it is recommended to use it in the way where the bottom of L is directed upwards in order to stimulate the perineum like in this picture



But in reality you may use and position it in any way that is comfortable and pleasurable for you, and with time and experimenting, you more likely to find the perfect fit.

Don't forget to apply as much lube as you can. It is a #1 recommendation for all types of anal play, especially when it comes to large toys.

Also, try to use the beads in the position you feel the most relaxed and comfy. Laying on the back, doggy, whatever you like, the main thing is you should be totally relaxed.

Don't try to insert the full length of beads at once. Do it gradually. When you get comfortable with one bead, move on to the next one. Your body will have time to adjust to the sensations and size, and this will help you to feel much more comfortable.