heres a few images of the filling loop. u will need to open the valve and let water in till the pressure gauge moves into the green, after this close the valve otherwise the water will over pressurise the boiler causing it to leak out.
theres a few images here but theres many types of filling devices. they are normally along the pipework into the boiler or under the boiler.
https://www.google.co.uk/search?q=baxi+filling+loop&espv=210&es_sm=93&source=lnms&tbm=isch&sa=X&ei=vkpYUoa4IKyM0wXflYDgCw&ved=0CAkQ_AUoAQ&biw=1366&bih=667&dpr=1#facrc=_&imgdii=_&imgrc=K0yUOXBcv4VxrM%3A%3Bse7FgNHTQmPm3M%3Bhttp%253A%252F%252Fi1.ytimg.com%252Fvi%252FobZK53tnaF4%252Fhqdefault.jpg%3Bhttp%253A%252F%252Fwww.youtube.com%252Fwatch%253Fv%253DobZK53tnaF4%3B480%3B360
kash, October 2013
