connecting four 8th notes

Use the beam palette (select the notes, "beam middle"), see: https://musescore.org/en/handbook/beams and for general settings: https://musescore.org/en/handbook/time-signatures#time-sig-properties

See https://musescore.org/en/handbook/beams#change-note-beaming or https://musescore.org/en/handbook/time-signatures#change-default-beaming

If they are truly four eighth notes, they should already be connected by default in most time signatures. Be sure you didn't actually enter quarter notes - if they are eighth notes, they should have either beams or flags on them. if they have neither, they aren't eighth notes, and you'll have to re-enter them as eighth notes. See the Handbook and/or tutorial videos for much more on note entry in MuseScore.