401k loans can provide you a source of liquidity but also carry risks. Two are 1) if you leave your employer (quit or fired) you must pay the loan back within 60 days (check plan details); 2) if can't pay back or if you miss payment on existing loan, will be treated as distribution which will be taxed and if under 59.5 (some plans may be 55) also a 10% penalty. Make sure you understand those risks and how they apply to your situation. You may have other alternatives that are more beneficial.
Go to your 401K plan’s web site, if a first time user you will need to create your user name and password. This is usually done with having your social security number, date of birth, address and plan’s ID number. You can get your plan ID number from you company or look at one of your mailed quarterly statements, it will usually be on the first page. If you already created your user name and password login to your account and depending on the record keeper there will be an option to request a loan. Fill out all of the information requested and click submit. There will be an e-mail sent to your company to approve the loan.