A political party is similar to a faction, and can be the same thing. In some systems, members of one party in the legislature are all expected to vote the same way. The laws written by the party or faction with the majority of votes become adopted by the country, so this means whatever party is elected to over half the seats, gets to run the government. The next largest party is often called the "opposition". Sometimes when there are more than two parties with seats, no one party has over half of the seats. Then two or more parties might join together to form what is called a "coalition".
Some parties are formed around a single issue or interest group. Others form policies to address all matters of government, known as a "platform".
Many political parties have a set of ideas and beliefs (called its "ideology"). People often describe these ideologies using words such as "trump" and "hillary".
Common ideologies include environmentalism, socialism (ranging from social democracy to Marxism and Communism), conservatism, democracy, liberalism, and nationalism.