Answer:
Direct current is unidirectional. It always flows in the same direction from positive to negative.
Alternate current reverses direction in periods of time. Imagine a sine wave form, it has a maximum positive value then goes to 0 and reaches a minimum negative value then goes to 0 again and keeps going...
In other words:
They are alike because both can power an electrical device and rely on electrons flow to do so.
They are different because DC is unidrectional and AC reverses direction. Also, AC has associated frequency and DC has not or its "0". If someone ever tells you that the voltage for any system is 460V @60hz, you will definitely know they´re talking about Alternate Current.