In a Multiparty system a single party sometimes may not secure the majority required to form the government. In such a case, some parties join together to form the government. Such government is called Coalition Government.

UK, USA

Single party system, Bi-party system, and multi-party system.

(i) the leader
(ii) the active members
(iii) the followers

(i) National Party: Indian National Congress, Bharatiya Janata Party, Communist party of India.
(ii) Regional Party: All India Anna Dravida Munnetra Kazhagam, Dravida Munnatra Kazhagam, Desiya Murpokku Dravidar Kazhagam, Pattali Makkal Katchi
(iii) Registered but unrecognized party: Labour party of India, Bhartiya Panchayat party, Indian Indira Congress.

Yes political parties are necessary for a democratic country because
(i) They are the backbone of democracy.
(ii) They are essential elements to form the government.
(iii) Citizens can elect their representatives.
(iv) Citizens also vote for the party of their choice and thus influence Government formation.

Criteria for A political party to be recognised as a National Party
(i) The party that secures should atleast 6% of the valid votes in Lok sabha election or assembly elections in four states.
(ii) They must win 4 seats in Lok sabha from any State/States
(iii) It has to win 2% of seats in Lok sabha from atleast 3 different states in the latest general election.

Functions of the Political parties:
(i) Provide: Loyal opposition, accountability & stability.
(ii) Nominate: Select and nominate individuals to elected office.
(iii) Organize: Organize political campaign, rallies and announcement of Manifesto to win public office.
(iv) Inspire: Put forward different policies and programmes for the welfare of the people.
(v) Co-ordinate: Connect the society and the state. Co-ordinate among members elected to office.
(vi) Govern: Form and run the government and develop public policy.