used to indicate the accompaniment of someone or something

used to indicate the means of achieving something

साथ

English Usage: I went to the store with my friend.

Hindi Usage: मैं अपनी दोस्त के साथ दुकान गया।

in company with

द्वारा

English Usage: The letter was sent by post.

Hindi Usage: पत्र डाक द्वारा भेजा गया था।

considering or containing

साथ-साथ

English Usage: We walked along the beach.

Hindi Usage: हम समुद्र किनारे साथ-साथ चले।

used to indicate partnership or union

मिलाकर

English Usage: This method works best in combination with other techniques.

Hindi Usage: यह विधि अन्य तकनीकों के साथ मिलाकर सबसे अच्छा काम करती है।