Sharing content on your home network is a pretty complex thing if it is a new subject but I will try and break it down.
First of all, your computer I assume is where all your media is placed. I normally try and make sure that all my movies/videos are in the same folder, same with music and pictures. This makes it easier when navigating in general.
Your computer itself these days usually is already pre prepared to share content over a network but usually requires some sort of manual intervention to make sure it works properly. The most straight forward option is to use Windows Media Player (going under the assumption you are using a Windows based machine). Have a look at the link below for more information.Have a read on the section - To turn on media sharing in Windows Media Player. What you are doing is turning your computer into what is called a "server".
http://windows.microsoft.com/en-US/windows-vista/Share-your-media-in-Windows-Media-Player-with-other...
Once you have done this, you should be able to access content on other devices providing they are connected to the same network. The easiest way to see this working is there is a DLNA app on the Tablet. At the top once it has found the servers, tap the one which is your computer/server which is normally represented by your computer name and program logo and then it should show you all the content stored on it.
In theory, it is as simple as that however this is where the rabbit hole gets deeper. The Digital Living Network Alliance (DLNA) was put together to help this process work. It helps share content between different devices regardless of brands but the most frequently asked question or issue seems to be file formats.
What you may find is when trying to play a certain video file/photo/audio file is that it is not supported or not recognised. You may find that the Tablet has no issues accessing the music and photos but problems with video.
When DLNA was originally setup, there was only one primary file format/extension for photo/music/video and there are hundreds of variants which are optional. Each client (product which is accessing the content) has a different list of supported extra formats which it may support. So if you have something which is not playable on your Tablet then it would indicate that it is not supported by DLNA or one of your devices. There are ways around this by using programs which have the ability to convert "on the fly" or transcoding into a format that you might be able to use/play. One that I found to work well to convert movies into a format that my TV recognised was "PS3 Media Server".
This whole media sharing and DLNA is a minefield for someone who has never given it a go but take your time when setting it up for the first time. I have tried to provide a simple explanation above and am sure that I have missed a few points but once you get it going, it is quite handy.
Hope that helps.
