Theoretically, spontaneous reactions can be used to obtain useful work. The Temperature must be in Kelvins. A process or reaction will occur spontaneously at constant T and P only if it is capable of doing useful work, i.e. G is negative. The free energy of the system must decrease. If G is positive the reaction as written is not spontaneous, but the reverse reaction is spontaneous.
H reflects the heat energy transferred between the system and surroundings.
T S is a measure of the change in the randomness of the system. The energy consumed or evolved with respect to the change in order of a system. The more negative H is, the more likely the reaction will be spontaneous. This reflects the drive toward minimum energy. This has caused more lost points than I care to remember.