As per the guidelines of CEFRL (Common European Framework of Reference for Languages) these are the things learners are supposed to be able to do once they are at the B1 level.
Listening: They can recognize the main points of clear standard speech on familiar matters regularly encountered in work, school, leisure etc. Also, understanding of main point of many radio or TV shows on current affairs or topics related to personal or professional interest when delivery is relatively slow and clear.
Reading: They can understand texts consisting of high frequency everyday or job-related language. Understanding of description of events, feelings and wishes in personal letters.
Spoken interaction: They can deal with most situations likely to arise whilst travelling in an area where the language is spoken. They can enter unprepared conversation on the topics that are familiar, or of personal interest.
Spoken production: They can interact in a simple way in order to describe the events and experiences, my dreams, hopes and ambitions. They can briefly give reasons and explanations for opinions and plans.
Writing: They can write simple connected text on topics which are familiar or of personal interest. They can write personal letters describing experiences and impressions.
In short, learners with a B1 level :
Can understand the main points of clear standard input on familiar matters regularly encountered in work, school, leisure, etc.
Can deal with most situations likely to arise while travelling in an area where the language is spoken.
Can produce simple connected text on topics that are familiar or of personal interest.
Can describe experiences and events, dreams, hopes and ambitions and briefly give reasons and explanations for opinions and plans.
The B1 level is prerequisite for asking for the French nationality. The B1 level can be proved with a DELF, TCF or equivalent certificate of B1.