Use ui.Chart.image.series() to print a time series, as a line chart by default, within a region:
// Load Landsat 8 top-of-atmosphere (TOA) input imagery.
var collection = ee.ImageCollection('LANDSAT/LC8_L1T_TOA').select('B[1-7]');
// Define a region of interest as a buffer around a point.
var geom = ee.Geometry.Point(-122.08384, 37.42503).buffer(500);
// Create and print the chart.
print(ui.Chart.image.series(collection, geom, ee.Reducer.mean(), 30));
Note that the arguments to ui.Chart.image.series() include an
ImageCollection, a region, a Reducer and a scale. Optionally,
specify coordinates for the X-axis. If these are not specified, the
system:time_start property will be used. (Make sure input imagery has this
property or specify the property to use.) The result should look something like
Figure 1.