Many people think that in order to meditate they have to sit in certain postures such as the lotus position. In reality it is just as effective, or possibly more effective, to sit on a chair or on the floor cross-legged, as you wish.
It may take you a few attempts, or a bit of moving around, to work out the best position for you. Some people find that sitting with their back to a wall can provide them with good support. You may also choose to sit on a cushion or folded blankets, but try to avoid sitting on a couch or sofa, as these do not provide good support for the spine.
Lying down is generally not the best position for meditation, mainly because there is a temptation to drift off to sleep, but do make sure that you are comfortable in whatever position you choose.
Once you have found a comfortable seated position, rest your hands flat on your lap, palms up, with your fingers gently outstretched. There is no need for any complicated finger positions.