DC offset

I'm working with a sensor and the signals I receive are varying sinusoids. I know the arduino ideally should only work with 0-5V...so here's my problem. How do I put the DC offset?

When working with a signal generator I mostly just do that with the settings. But How do I do it with a sensor? Do I explicitly need to use a battery?

"Sinusoids" does not equal "Half cycle less than zero volts".

Delta_G:
In order to answer that question, one would first need to know the nature of the signals from this yet unnamed sensor.

It's a HB100 Doppler Sensor

KeithRB:
"Sinusoids" does not equal "Half cycle less than zero volts".

Right. Well under the oscilloscope half the cycle does go below zero.

N-XIGE:
Right. Well under the oscilloscope half the cycle does go below zero.

Is the oscilloscope in DC mode?

The AC nature of the signal is the least of your problems. From the datasheet:

"The magnitude of the Doppler Shift is proportional to reflection of transmitted energy and is in the range of microvolts(μV)."
and
"A high gain low frequency amplifier is usually connected to the IF terminal in order to amplify
the Doppler shift to a processable level (see Annex 1)."

A very quick Google search revealed plenty of helpful websites. This one in particular goes into detail about the amplifier/filter design. It does look like you will need to offset the output but like KeithRB said, I think the offset may be the least of your problems. Maybe scrap the idea of using the module directly and spend a couple of bucks to get one a breakout board like in the link above.

If he really just wants the Doppler shift and the magnitude is irrelevant, he only needs to get the signal to a logic level, rectify it with a single diode and clip it to 4.5 V or so. He can then determine the frequency from the pulses.