Contractions are shortened forms like don't for do not. They are standard in everyday speech and casual writing, and usually avoided in highly formal or academic writing. They are not wrong, just casual, so the setting decides whether they fit.
Texting a friend, I can't make it tonight feels natural. The same message in a memo to a client would usually read I am unable to attend. The contraction is not wrong, just casual, and formality depends on who is reading.
A blog post can say it's easier than you think and feel friendly. A research paper would usually prefer it is. This caution also covers contractions after nouns, names, here, there and question words, like Mary's or here's, which formal writing usually spells out as Mary is or here is.
The Chicago Manual of Style endorses contractions in most prose, with a caution against overuse, so it's and don't are not errors, just choices to keep in check.
APA is stricter. It advises avoiding contractions in formal academic assignments such as class writing, theses and dissertations, though even APA frames this as context-dependent, not a fixed rule.
The MLA permits contractions in its own scholarly publications, showing style guides do not all draw the line the same way. When in doubt for academic work, leave contractions out; elsewhere, use them freely.