Gesproken Nederlands (spoken Dutch) and geschreven Nederlands (written Dutch) differ significantly. Spoken Dutch uses contractions and reductions that never appear in writing: ik wordt often reduced to k, jij to je, dat is to das, wat is to was, hebben to hewwe in informal speech. The word even is constantly reduced to ff in text messages and ff in speech. These reductions are normal, not sloppy — they are the genuine phonology of colloquial Dutch.
Grammatical differences: in spoken Dutch, the simple past (imperfectum) is largely replaced by the perfect (perfectum). Ik heb gisteren gewerkt (spoken) rather than Ik werkte gisteren (written/formal). Relative pronouns: in speech, die is used for both de-words and het-words (het huis die ik kocht — incorrect in writing but common in speech). Sentence-final particles and modal particles (toch, maar, dan, eens) appear far more in speech than in formal writing.
Vocabulary differences: spoken Dutch uses more loanwords from English without hesitation (ik ga even checken, het is een issue, we moeten dit soonish oplossen). Written formal Dutch uses official Dutch vocabulary (controleren, probleem, snel). Intensifiers used in speech: echt, hartstikke, knetter, super, mega — these soften or strengthen adjectives informally but would not appear in a formal report. Knowing both registers allows you to read newspapers and write professional emails while also understanding natural spoken Dutch — two quite different skills that require different exposure and practice.