Look at these http://www.dctorrent.com/showthread.php?t=72676 - The 4gb rule
What is seed, leech and torrents - http://www.dctorrent.com/showthread.php?t=627
http://www.dctorrent.com/showthread.php?t=64052 - Complete download with utorrent
Ways to increase your ratio - http://www.dctorrent.com/showthread.php?t=37373

These are just some of the helps that is available on the guides/tutorials in the site assistance section.

You have mentioned that you are trying to download a video of 70mb. Tell me what kind of video this is, if possible tell me what section it's from e.g. Drama's, music etc.

The ratio thing is very simple. In DC we like to share and the simplest way to do that is seed whatever we download 100% e.g. If you download a music torrent which is 100mb than you should upload that torrent till you reach 100mb or 1.00 ratio on that torrent.
It is essential to maintain a good ratio of 1.00 at least as we heavily rely on people to share otherwise there will be no one seeding the torrent and it will be dead.

You have downloaded a part of the desi drama called love story. You should immediately, log on to DC and go to music section. Look through it and download as much music as you can and seed it as much as you can as well. The music torrent is a ratio free torrent, so only your upload will count towards your ratio and not your DL. You can do that will sports torrents or documentaries as well.

Just because music is a ratio free torrent that doesn't mean that you wouldn't upload 100%, UL as much as you can even more that 100%, as you need at least 4gb to download movies, desi drama etc.

So, ratio is just your stat of Download and upload at DC. A ratio of 1.00 is healthy to survive at DC, with the ratio free torrents you download, only your ul will increase, so your ratio would increase. Also refer to the threads i have shown in this post.

Hope this helps.