What is USA's position on the Israeli-Palestinian conflict? Are they neutral? Are they trying to end the conflict, or help one of the parties? If not, why do they support one side?
As the US is not a politically monolithic nation, there is no monolithic stance shared by all officials on all issues related to Israel. However, there are a number of issues regarding which US policy has been consistent through various administrations and Congresses.
Particularly since the 1991 Madrid Conference, the US has actively sought to resolve the Israeli-Palestinian conflict via a Two-State solution, that would create a Palestinian state. Historically, the United States has advocated that the borders of the new Palestinian state be defined approximately by the 1949 armistice lines, with some changes made to accommodate Israeli settlements. The Clinton Parameters called for the creation of a Palestinian state in the entirety of Gaza and almost all of the West Bank, and Obama called for the borders of the Palestinian state to be defined by the 1949 armistice lines with "mutually agreed [land] swaps".
The US condemns Israeli settlement construction. A number of administrations and officials, including George W. Bush, Obama, and Bill Clinton condemned Israeli settlements, operating on the belief that settlement construction poses an obstacle to the implementation of a two-state solution. The Obama administration has tended to support Palestinian demands that Israel halt settlement construction as a precondition to final status negotiations, pressuring Israel to halt construction before the 2010-2011 talks and 2013-2014 talks.
The several decades, the US has been granting military aid to Israel, most of which is spent on American military hardware. The US has also sent aid to Palestinian areas as well, in an attempt to combat extremist elements and meet humanitarian needs.
The US often sides with Israel in the UN, following the policy that the US will veto resolutions condemning Israel that do not also appropriately blame other parties to the conflict. You can read more about the UN's relationship with Israel here and here. The US' policy is intended to counteract substantial focus on Israel by other UN bodies, like the General Assembly and Human Rights Council.
The United States usually supports Israel's military operations in general terms, but often condemns specific actions taken. For example, during Operation Pillar of Defense, Samantha Powers (US representative to the UN, appointed by Obama) condemned Israel's targeting of Hamas militants in UN schools, and George W. Bush condemned an Israeli attack on [Hamas' then leader] during the Second Intifada.
You may notice that most of these stances are very recent, usually not extending back further than the 90s. This is because, over the course of Israel's history, the nature of its conflict with its neighbors has changed. Earlier in Israel's history, Israel was often attacked by a number of nations at once, each of those nations possessing armies. In 1949, the newly created state of Israel was attacked by many of its Arab neighbors. Israel was again attacked by Egypt, Syria, and Jordan in 1967, and another time by Syria and Egypt in 1973.
However, since then, Israel has dealt less with nations and their armies, and more with terrorist groups. Furthermore, in 1993, Israel transferred control of some areas to the Palestinians, and agreed that a Palestinian state would be created as the result of negotiations between Israel and Palestinian representatives. Therefore, most American policy towards Israel nowadays deals with issues that have been a part of Israel's history for a while, but have become much more prominent due to recent developments like the transfer of control over Gaza and some areas in the West Bank to Palestinians.
You may also be wondering why the US has an interest in the area at all, in which case you should take a look at this question on the Politics SE, which addresses exactly that question.