let me in with my english.... he he
'razdetsia', 'ya razdenous'...
in russian lots of verbs can be reflexive
'-sia' at the end means 'self', or to make something by self
but not always the diference is clair.
раздеть - undress (someone)
раздеться - undress self, to get off one's clothes
стучать - to knock (on something; like at the door, on the table, etc)
стучаться - to knock [at the door]
with the door there is no difference, you may say:
он стучит (в дверь) = он стучится (в дверь)
but with the table, etc, you can't use стучаться, only стучать.
-ся (or -сь) is just added at the end:
я стучу - я стучусь
ты стучишь - ты стучишься
он стучит - он стучится
мы стучим - мы стучимся
вы стучите - вы стучитесь
они стучат - они стучатся
- - -
with раздеть there is a problem. Russian verbs have or belong to two aspects: perfective aspect and imperfective aspect. This is not a tense or conjugation this is the aspect of the verb itself. Every verb is either perfective or imperfective. Perfective verbs don't have present tense, but only past and future tenses. But imperfective have only past and present tenses (future tense could be formed with them but in a different way using the verb to be, which is not used in conjugations usually). Seeing this picture some foreigners say simply that thre are 5 tenses in Russian. But we are sure there are only three. And aspect is the aspect. Aspect is seen in infinitive.
Раздеть is a perfective verb. Imperfective verb with the same meaning is раздевать. You may say Russians have a pair of verbs for every meaning - perfecvite and imperfective to cover all three tenses.
Aspect is the thing called tense in English. In English no differnce is made between tense and aspect. They call both of them tenses. There are perfect tenses and e.g. indefinite tenses. And every verb can be used with both of them. But in Russian verbs themselves are either perfective or not. This feature is not added conjugating the verb. This feature belongs to the verb itself.
We divide between aspects this way - perfective verbs in infinitive answer the question: что сделать? (~ what will have done?), but imperfective: что делать? (what to do?)
Perfective and imperfective verbs usually have the same stems, and aspect could be formed by adding prefixes or suffixes.
E.g. the verb write - писать is imperfective.
to make it perfective prefix is added - написать.
Perfective verbs could be made imperfective adding suffixes:
записать - to write down (perfective; but with another prefix)
записывать - to write down (imperfective)
If to compare with English tenses -
Indefinite tenses coincide with imperfective verbs usage
Continuous tenses coincide with imperfective verbs usage
Perfect tenses coincide with perfective verbs usage
Perfect continuous tenses coincide with imperfective verbs usage
something like that. But i'm not sure.....

There is such a mess in Russian grammar...
пока.