Car dies

My must just completely died on me. There wad no
clicling sound no nothing just dead. What
happened was that i went in a shop for like 15
mins and when i came back and put the key in the
ignition all the lights did turn on like they usually do
but when i turned the key it made a weird sound i
turned the key a couple of times it made the same
sound and then it was completely dead no lights
no nothing just plain dead. This had happened to
me before so i kind of knew how to get the car
started. What i did was i brought a jump cable
conected one of the two wires to the red terminal
of the battery and as soon as i conected the other
wire to the black terminal it sparked and the car
lightd in the car lit up and i took the jump cable off
of the battery and the car started normally.

Note : i did not connect the other end of the jump
cable to anything i had the other end in my hand
and i had made sure that they are not touching
each other.

Although my carvis working perfectly now butvi
would like to know what caused this problem as it
had happend before only once probably a month
back.