Not everyone can meditate cross-legged — I’m one of them!
Fortunately, there’s no need to be in a cross-legged posture to meditate. In fact if you force yourself into an uncomfortable cross-legged posture then you may do long-term damage to your joints, and you certainly won’t be comfortable enough to meditate effectively.
However, if you have the flexibility then sitting cross-legged is a very stable and grounded posture. There are a number of ways of sitting with crossed legs.
The first picture is the tailor position, which is the simplest cross-legged position. It’s also probably the most common cross-legged posture.
It’s very important for you to have both knees on the ground, to give you adequate support. Having three points of contact (your butt, and both knees) gives you a lot of stability. When was the last time you saw a photographer trying to keep a camera stable on a dipod?
If you can’t quite get both knees on the floor, then you can use some padding (a thin cushion or folded scarf) under your knee to keep you stable. If one, or both of your knees is more than an inch (2-3cm) off the ground, then use a chair or try sitting astride cushions or a meditation bench or stool. You can always do some yoga to loosen up your hips, and then come back and try a cross-legged posture later.
Again, if your hands don’t rest naturally on your lap, keep them supported, perhaps on a cushion or on a blanket. You might want to alternate which foot is in front from time to time. This is a good thing to do because any cross-legged posture is slightly asymmetrical. If you alternate the position of your feet, then you’ll even out the imbalances and not “build them in” to your posture.