A significant amount of time in Mass Effect is devoted to conversations with other characters. This is done through the "conversation wheel" that appears near the bottom of the screen whenever your character has the opportunity to say something. All dialogue in the game is fully voiced, including that of Commander Shepard. Rather than choosing the exact words your character will say however, Mass Effect shows you several options on the wheel corresponding to general feelings, questions, or emotions. These short phrases are then turned into full lines of dialogue that are spoken by your character.

To select a dialogue response on the Xbox 360, hold the left analog stick in the direction of the choice you wish to select, and then press the A button. You can also press the X button instead, which will begin your character's line immediately, stepping on the lines of any character who is speaking at the time. X is also used to skip dialogue if you wish to do so. On the PC you use the mouse to select dialogue options, and the Spacebar to skip dialogue.

The dialogue wheel itself is divided into six sectors. Choices on the wheel's left side usually give you more information about a given topic, while choices on the right tend to bring the conversation closer to its conclusion. Additionally, the top of the wheel tends to correspond to the Paragon path, where your character makes cooperative and unselfish decisions.
The bottom of the wheel typically corresponds to the Renegade path, where your character makes decisions that are more selfish and impatient. This is not always the case, but it is a good general guide to framing your responses during a conversation if you wish to play as an honorable (or merciless) character.

Sometimes you will see the option on the middle left to "Investigate."
Selecting this option brings up more choices for topics of conversation, and the orientation of these choices often does not correspond to the Paragon / Renegade paths described above.

If you have spent sufficient talent points in the "Charm" or "Intimidate" talents, you will sometimes also have the option to persuade characters to achieve a nonviolent outcome or to give you additional money, items, or information. These choices appear in the upper and lower left quadrants as blue and red dialogue choices respectively. If you lack sufficient skill in these areas, these choices will be grayed out, and you will not have the option of using them.