One of the most complex (and fascinating) aspects of learning Ukrainian is understanding the rules relating to word stress and putting them into practice in the spoken language.
The late George Y. Shevelov, one of the most insightful Ukrainian linguists of the 20th century, wrote:
[Ukrainian] preserves free dynamic stress [...] , which can fall on any syllable and which can shift within a paradigm. The distribution of paradigms with fixed and with shifting stress is unpredictable unless morphological rules interfere.
[chapter on 'Ukrainian' in The Slavonic Languages, ed. by B. Comrie and G. Corbett (London, 1993)]
This site addresses the issue of stress in Ukrainian and is aimed at learners of all levels, from beginners to advanced. First-time users are encouraged to begin by reading the Introduction.