Whilst I love Bertie Russell’s "History of Western Philosophy" and would highly recommend it, it’s more a compendium to be used complementary to an inquiry rather than an exercise in itself. The devil is in the detail for philosophy and a good philosophical dictionary might be more useful to you.
You shouldn't be put off of Plato, along with Aristotle he underpins the majority of western philosophical thought so will form a basis for any further reading. Start with something like "The Republic" it's one of his most accessible works and the majority of editions come with a supporting essay. There is a good translation by G. M. A. Grube or if you want one with an example of a controversial interpretation (although not one that I particularly agree with) try Allan Bloom. If you needed additional help with the text Routledge have a comprehensive set of relatively objective and easy to understand guides without being "...For Dummies".
