Introduction

cum + ablative means 'with'.

cum can also be used with verbs to mean 'when, since, although, whenever'.

Basic rules for translation

cum + indicative'when', 'whenever'
cum + subjunctiveprobably 'since' (only try 'although', 'under the circumstances', etc. if 'since' does not make sense)
cum + subjunctive + tamen'although'