"Please call the teacher."
There are several tenses for verbs in japanese.
呼ぶ (yobu) is the dictionary form of this particular word.
呼んで is yobu conjugated into て form (which is a form typically used when issuing directions or asking someone to do something.
呼んだ is the past tense of yobu. This form is also referred to as た form because all past tense conjugations end in た or だ.
呼びます is yobu in it's masu form, also known as the polite form. Godan verbs such as yobu have their u-endings become I sounds in this form such as [kaku 〉kakimasu].
For a better grasp of this concept, I recommend the application "Conjugation Japanese" to aid you in your studies. It's free and easy to use.
Also, it's important to remember that we use て form here because 下さい (ください) is actually the Command Form of くださる (下さる). The Command Form (命令形, meireikei) is used to command someone to do something (e.g. 止めろ！yamero! Stop!, 死ね！shine! Die!, 放せ！hanase! Let go!)
We are connecting the verb 呼ぶ to the verb 下さる, so we use the て form of 呼ぶ, 呼んで.
Both are different declensions of yobu (to call, to invite, to cause). Yonde is usually used when instructing someone to do something. It is generally known as the 'te' form of verbs but some take the ending 'de' instead as this one does. Yobi in exactly in that form (the yobimasu with masu removed) I believe would be used when it features first and followed by another action as we have seen elsewhere in this part of the course.
It's easier if you check the plain forms.
呼ぶ → 呼んで (godan verb/ "u verb")
浴びる → 浴びて (ichidan verb/ "ru verb")