I am looking to start investing but only am able to invest about $100 a month. I am thinking about going with ETF is to start off and would like some advice on how to get things going. Thanks in advance!

Open a brokerage account. Paper trade before u invest real money.
Decide ur risk tolerance. Attend tutorials either online or at the brokerage office. Go to the library & start reading investment books. Learn before u commit real funds- what stocks will u pick, what is ur time frame, when will u exit if u lose $, when will u take profits--these r all the things u need to know. Starting with a $100 a month is a great plan, but u need to learn before u can earn. Different brokerages have specific minimums u must have in ur account before u can trade. Be sure u can afford to lose the money, do not invest funds u can not afford to lose, if u have to live on it, u r not ready. Good luck & l hope u r profitable fast!
Good luck.

Forget stocks and ETFs. FInd a good no-load mutual fund and set up an automatic purchase plan. WIth stocks and ETF is the commissions will kill you on small investments.