Both start by making an assumption, also known as an hypothesis — in scientific parlance it is an educated guess as to the factual root cause of an observed effect(s). Now at this point, the scientist seeks to discredit the hypothesis through conducting tests and/or observations. In short, the scientists eliminates the possible and whatever remains, however improbable, is the truth.
The pseudo-scientist on the other hand rarely conducts any test, but rather tries to connect together random data points in hopes of revealing a correlation as proof of causation. In other words, a pseudo scientists can “prove” as “scientific fact” nearly any random set of coincidental happenings as cause and effect. For example, a pseudo-scientist could argue quite well that if someone wears red slippers and counts to 100 before bed every night, this will cause rise in the morning. And if they are truly steadfast in wearing those slippers and counting every night, no doubt they will “prove” this is the cause of the sun rising because, well, the sun will rise (though obviously for a very different reason). It maybe a stupid example, but the principle applies to real complex scientific debates we are currently having.
So, there you go. Pseudo-science versus actual science. Be prepared, be skeptical. Remember a good scientist is someone who is constantly questioning themselves. They are not convinced of being right very easily.