Question: How do you conjugate in German and English two reflexive verbs such as, sich + vorstellen?

Answer: Conjugating Reflexive German Verbs

To fully conjugate a verb in any language you need to be aware of all the possible persons who could be doing the action of the verb. In English they are I, you, he, she, one, it, we, and they.
In German they are as follows:
Ich = I, du = you(familiar), er = he, sie = she, es = it, man = one, wir = we, ihr = you(familiar and plural), Sie = you (polite, singular & plural), sie = they.

There are more possibilities in German, especially when using 'you'!!

With regard to the verb sich vorstellen, which in English translates as 'to introduce oneself', you need to also use a reflexive pronoun. A reflexive verb is an action one does to oneself. Other examples might be (in English) to wash oneself, to dress oneself, to look at oneself in the mirror.
The English conjugation of 'to introduce oneself' would be:
I wash myself
You wash yourself
He washes himself
She washes herself
It washes itself
One washes oneself
You wash yourselves (more than one person)
We wash ourselves
They wash themselves
There is a particular reflexive pronoun for each.
Sich vorstellen is a regular reflexive separable verb. Use the regular verb endings (I'll put them in italics) plus the appropriate pronoun (I'll put those in bold print) and the separable prefix vor will always go at the very end. Here it is:
Ich stelle mich vor = I introduce myself
Du stellst dich vor = you introduce yourself (familiar & singular)
Er stellt sich vor = he introduces himself
Sie stellt sich vor = she introduces herself
Es stellt sich vor = it introduces itself
Man stellt sich vor = one introduces oneself
Wir stellen uns vor = we introduce ourselves
Ihr stellt euch vor = you introduce yourselves (familiar & plural)
Sie stellen sich vor = you introduce yourself/you introduce yourselves (polite)
Sie stellen sich vor = they introduce themselves.

Remember that unless you are actually starting a sentence with these, only the last but one (polite 'you') would have a capital; the others, including 'I' all use lower case letters in German. If you were conjugating a verb such as 'sich waschen', which means 'to wash oneself', you wouldn't have the additional problem of the prefix. Do beware, though, that many German reflexive verbs use prefixes such as 'an', 'aus', 'um', 'ein', and 'ab'. If in doubt, check in a bilingual dictionary that will tell you. The abbreviation vr means reflexive verb and sep means a separable prefix. Complicated stuff!