"My toe is aching."
Translation:मेरे पैर की उँगली में दर्द हो रहा है।
Both रहा and है are something called 'tense auxiliaries' and can't exist by themselves. They have to be attached to another verb. रहा tells us that the verb is continuous (similar to adding 'ing' in English) and है tells us that the verb is in the present tense. Here, होना (to be) is used as the main verb to which the auxiliaries are attached.