Hello - welcome to the forum.
I don't own the DP-03SD - although I do own it's bigger cousin the DP-32SD. Seems like there are a couple of people here who either currently use that recorder or did at one time. We'll see if anyone shows up who has first hand experience.
Short of that - there are a good number of user tutorials on youtube for the Tascam DP-03SD - see the link below. When I first acquired my DP-32SD about 11-12 years ago - I immediately watched a bunch of youtube videos to help me get familiar with the machine and to help get me started with it.
Click here:
There's a bunch of people here who may be able to with more general home recording advice.
There's also a dedicated website for Tascam related products including the DP-03SD - see the link below:
An audio engineering, recording, and songwriting community, we have been a valuable resource for TASCAM hobbyists and professionals for almost 30 years.
www.tascamforums.com
Good luck!