If you search on "kiza" or "seiza" you will find plenty of instruction
I find this makes my toes ache until they are numb. You can also flatten your feet straight back, which is easier sometime, but more of my legs go numb that way and it is hard to rise from even without the numbness.
I once maintained this position through a lengthy dinner (over an hour) because a waiter was insensitive enough to say that as a westerner I shouldn't try to sit that way - "too difficult".
If looks could kill........
I can be rather stubborn at times and this was quite comfortable for me, but these days (20 years older) I don't think I could ever do it again
If you have poor circulation, damaged knees or thick/heavy thighs, opt for a less formal modified lotus position. Standard lotus is cross-legged with the feet atop you thighs; modified leaves the feet under the thigh (sometimes uncomfortable on a hard surface).