The "qualifying event" --termination of employment-- happened just recently?
You select your IRA custodian. This might be a discount broker or a mutual fund company. If you expect to invest in funds, pick the fund company. If you plan to invest in individual stocks, pick a discount broker.

Shortly after termination of employment you receive forms from the company managing the 401k. They ask you to choose whether you want to leave the money with them, take cash, or transfer it. You indicate transfer it. You fill in the name of the new IRA custodian you have selected and return the paperwork.
It may be several months later that the 401k folks write a check for all your money in the account. It is important that check NOT be written to you. It should be written directly to your new IRA custodian. They can mail the check to you or the IRA custodian, that doesn't matter.
When that transfer of funds has occurred, you call the new custodian and make your investments.
Takes some time, because the 401k company may be real slow with the paperwork.
Best wishes, Chris