Once you become a Participant (for so long as you remain employed), or if you are an eligible employee still within the waiting period, you may be permitted to deposit into the Plan distributions you have received from another retirement plan or an IRA.
Your plan's rollover form can be found on the web under "Documents & Reports" - "Forms & Notices" - Transfers
The first page should be filled out and returned to your plan sponsor.
The second page has information on how to make the check payable to your plan's custodial bank. Failure to follow these payment instructions may result in delays.