trust nobody
but barring that plan..
You can use a hex editor to view some items.
You can also use a port scanner to view if any details are being sent to the internet and what is being sent.
Having the source code and compiling the exe yourself is the only sure way for a novice.
Some programs count on the wide spread use of the program to trojan you.
for example, someone might attempt to steal a password or open a hole , install a keylogger etc. Log the info to files hidden on your computer and then hope at some point you either use another program or view a webpage that downloads the information encrypted so you think the item is safe.