Where do I start?
If you are new to Galaxy then start with one of the introductory topics. These introduce you to concepts that are useful in Galaxy, no matter what domain you are doing analysis in.
If you are already familiar with Galaxy basics and want to learn how to use it in a particular domain (for example, ChIP-Seq), then start with one of those topics.
If you are already well informed about bioinformatics data analysis and you just want to get a feel for how it works in Galaxy, then many tutorials include Instructions for the impatient sections.