老师 means teacher. 师资 means more like a kind of resource or a quality of a teacher. 资 is from the word 资源 whereas 师 is from the word 老师. To combine these two words together has a connotation of the phrase a quality of a teacher. Have a nice day and hope this helps.

老师代表一类人；师资代表一群老师的教学质量，属于一种资源。如，这个学校有100位老师，这个学校的师资力量是这个城市最好的。

老师 equals teacher 师资 equals teaching force

老师是一个职业；师资，比如说某学校，指这个学校整体老师的教学水平。

(1)"老师" : means a teacher, such as "I am a teacher(老师)". In China，we don't call our teacher Miss XX or Mr. XX. All are called "XX老师" such as "李老师" no matter men or women. You can also call your teacher "老师" directly without their Lastname in the front. (2)"师资" means qualifications, the comprehensive ability of teachers.