To the left - list of techs available for research. Below this list you can see number of turns need to complete selected project. To the right you can see that gives you selected tech. Social projects - buildings, wonders and trade goods. New Modules - starbase modules. Military projects - ships. Abilities - bonuses you gain instantly then you completed researching this tech. Future research options - my english isn't that good

Well, say, in both 'Phasers' and 'Photons' technologies you can see 'Corvette Technology' in Future research options. It means that you need both 'Phasers' and 'Photons' to research 'Corvette Technology'.
Better to see tech tree in tree form - see 'JavaScout's Galactic Civilizattions Database 1.01.029' in GalCiv Forum
~SDC~