Welcome! Notation such as Bb/F is known as lead sheet symbols or chord symbols. For jazz players and musicians with good theoretical knowledge and understanding of chord construction, this notation serves as shorthand and communicates a lot about the song's progression and the nature of each chord.
Rather than reading the printed notes verbatim, a pianist can follow the melody and improvise an accompaniment based on the chords outlined in the lead sheet symbols. The notation can be variable, but not too complicated:
The first part is the note name of the root of the chord. For example, Gm7 indicates that we're building a chord with root G.
M or m indicates major/minor. You might not see the big M for major, and you might see "maj" for major and "min" for minor. You may also see things like m11 (minor eleven) or maj7 (major seven), and the added numbers indicate chord extensions (which is a separate topic entirely).
Lastly, slash notation (e.g. Bb/F) tells you what note to play in the bass (left hand on piano). Bb/F is the major chord Bb (Bb, D, F) played in second inversion with an F in the left hand.