What do you mean by power rating of an electrical appliance? How do you use it to calculate the resistance of the appliance?

What do you mean by power rating of an electrical appliance? How do you use it to calculate the safe limit of current in it, while in use?

Two lamps, one rated $220 \mathrm{V}, 50 \mathrm{W}$ and the other rated $220 \mathrm{V}, 100 \mathrm{W}$, are connected in series with mains of voltage $220 \mathrm{V}$. Explain why does the $50 \mathrm{W}$  lamp consume more power?

When a current $I$ flows through a resistance $R$ for time $t$, the electrical energy spent is