B1: the level where Spanish starts working
B1 is the point at which you stop falling back on English. You can deal with most of what a trip throws at you, follow a conversation that is about you, and explain what you think rather than only what you want. For most learners it is the first level that changes anything.
What B1 actually lets you do
At B1 you can handle a hotel problem, a doctor's appointment or a disagreement about a bill without switching language. You can tell a story in the past, say what you would do, and follow a film with a bit of effort. You are not fluent, but you are independent.
How long it takes
Spanish is one of the fastest languages for an English speaker to learn - the American Foreign Service Institute puts it in its easiest category. B1 usually lands somewhere around three to four hundred hours of real study, which is a year at an hour a day with weekends off.
Twenty countries at once
What makes B1 worth aiming at in Spanish specifically is the size of the reward. Twenty countries use it as an official language, and at B1 all of them become places you can travel in properly rather than around. No other single level opens as much ground.
What it is worth on paper
On the certificates, B1 is DELE B1 or roughly 750 to 865 on SIELE. It is also the level most Spanish universities want from exchange students. If you need a certificate for nationality rather than study, note that the bar there is A2, one level lower.