Setting a goal of learning polite expressions and basic working vocabulary is not so hard, and it can be a lot of fun. National and regional differences in vocabulary do exist, but they are minor, probably involving less than ten percent of the words used in Spanish. Nations and regions do incorporate some of the native tongues into their Spanish. For instance, seaweed is alga marina in most Spanish-speaking nations, while in Chile we use the native cochayuyo for edible seaweed. While for the most part differences in vocabulary simply give rise to a little humor, once in a while they can give offense.
Most native speakers know to adjust their understanding and use of vocabulary accordingly.
Differences between Spanish-speaking nations are underscored when slang is used, and minimized when a more formal Spanish is utilized. Differences in accents are much more pronounced than divergence in vocabulary. Accents are easy to pin down, however. I was speaking to someone in English and an observer who overhead the conversation asked if I was Chilean, just from the way I spoke English. I am asked this question often.