Greetings

HELLO:The word “Hello” was originally used as an exclamation to call attention, an expression of surprise, or a greeting. Thomas Alva Edison used “Hello” for the first time as a telephone greeting instead of Alexander Graham Bell’s “Ahoy”. Hello is also pronounced as “Hullo” in some parts of the world . 
HANDSHAKE: In ancient times handshake was a gesture of peace to show that there are no weapons. In recent times it is a ritual between two people when they meet and greet each other.
NAMASKAR/NAMASTE:Namaskar/Namaste is an Indian way of saying hello. While doing Namaskar/Namaste we join our hands and bow. In India we bow to show respect.
TOUCHING FEET: Also known as "Charan Sparsh" means to touch our elders feet. In India it has been a custom to touch our elder's feet and seek their blessings on auspicious occasions.
SAYING IT WITH FLOWERS: Welcoming a guest with a bouquet of flowers is global custom. In India and several Asian countries it is customary to welcome a guest with a garland of flowers placed round the neck. In weddings too floral bouquets and garlands play a significant role.  

CUSTOMSWhat do we mean by customs? 

Customs are laws or rules which are not written but are practiced since ancient times and are passed on by our ancestors to us: it is any thing that people do and have done since long times and are practiced every day or on specific occasions.
Some people define customs as habits, but these two words and their meanings are different. Habits are things we 'like to do' and Customs are things that we 'have to follow'. When a custom is handed over from generation to generation and practiced in the same manner as before ,it becomes a tradition.The custom of worshiping Lord Ganesha (elephant God) before beginning any important function/ event, was considered to be auspicious in the past which has become a tradition in India over the years.

RITUALS: How are rituals different from customs?

Rituals are distinctly different from customs.  Rituals are rites /procedures which are performed according to prescribed rules/customs.Ceremonies are also rituals with a purpose/sacredness. If a ceremony lacks intention it becomes a "meaningless ritual". 

Here is an example to differentiate between festival,custom,tradition and ritual.
Diwali is a festival of Hindus; celebrating Diwali is a custom; over a period of time, generation after generation people have been celebrating it, therefore celebrating Diwali has now become a tradition; the procedure of performing the Pooja (worship) on Diwali, i.e., Ganesh Pooja, then Laxmi Pooja, is called ritual.

In this way festival,custom,tradition and ritual are the beads that make a single garland.