The wrap is tied at the waist or hips and can be spread to the buttocks or up to the belly. Tying the knot is done without using your legs, only the upper part of your body is active.
There are apparently no reasons not to use and tie the wrap sitting down.
You can use it just as described on the instruction booklet or on the online videos.
Remember that you will need a bit of room behind you and on your sides while you tie the wrap.
This wrap is interesting because its fabric molds to your body and can be spread without any uncomfortable bulks.
When the baby is about 4 months he can squat and his legs will come on each side of your upper body. Your chair needs to be wide enough.
When he reaches 6-8 months he'll be bigger in a front carry and his feet will go all the way to the back of the chair.
The best time to use the wrap is during the first months, when baby's not too big, doesn't wriggle and can be worn several times during the day.
A ring sling may also be an interesting carrier for you as your child gets bigger. It is very fast to put on but allows only one-shoulder carries.