There's no need to fill out the memo field when you transfer XLM into your StellarX account. At least not on our end of things—if you're sending us funds from a custodial exchange or other wallet, please check with them. Many exchanges do require a memo for outgoing transfers.
If you're sending us XRP or XEM via Changelly, you need to follow instructions to attach a destination tag (XRP), or message (XEM) to your outgoing transfer. The Deposit flow will walk you through it. It’s just an extra piece of information you copy and paste along with the destination address.