The present-tense forms of the verb होना-'to be' (ie, है,हैं, हूँ, हो) are used as present-tense markers for other verbs. Similarly, the verb रहना (to stay) marks the continuous aspect (for past, present and future tenses).

मैं खता हूँ - I eat - Simple present
मैं खा रहा हूँ - I am eating - Present continuous
मैं खा रहा था - I was eating - Past continuous [था is the past tense form of होना which marks the past tense for all tenses except the simple past]

In most cases, the simple present and the present continuous tenses correspond pretty well with their counterparts in English. Habitual and repeated actions are indicated with the simple present tense in Hindi as well.

The confusion arises mostly in the case of stative verbs and this is likely why some Indians overuse the continuous aspect. For stative verbs (like 'know', 'understand', 'hear' etc), English does away with the present continuous and uses the simple present instead. However, Hindi does not consider many of these verbs as stative or uses nouns/adjectives in their place. So, Indian ESL speakers are often confused as to why these verbs cannot be used with the continuous aspect leading to sentences like 'I am knowing her' or 'I am understanding'. Note that, while common, this usage is considered wrong in Indian English as well.

Another instance of present continuous overuse that is much more tolerated in Indian English is related to the present perfect continuous tense (have/has been ---ing). Hindi also has a corresponding tense but since it is considered formal (and perhaps a little pretentious), the present continuous often takes its place. So, you see sentences like 'I am waiting since one o'clock' translated literally from 'मैं एक बजे से इंतज़ार कर रहा हूँ' .