My brother passed away last week. he has a will leaving everything to myself, his sister. he has one checking account, no home, a car, and a life insurance check written to him. What is my next step?

Much of what you can do or should do will depend on the value of your brother's estate and the entity which controls the asset.
If his car is paid for, then you should be able to go to the local DMV and get form called an Affidavit of Heirship to transfer the vehicle into your name.  This is basically where you swear and affirm that he left everything to you.
Life insurance policies should pass directly to whoever is listed as the beneficiary.  If no beneficiary is designated, then the insurance company may want you to file a probate action and obtain a judgment to tell them who is actually the heir.  
When it comes to checking accounts, may banks will also require a probate for the same reason.  They are mainly looking to prevent any liability on their end for giving an asset to the wrong person. 
If the estate (i.e. funds in the bank account and his personal possessions) are worth a great deal of money, then a probate is cost effective.  If the estate if very small...(i.e. under a couple of thousand), then a probate may not be very cost effective.
A probate is basically where a judge reviews the Wills and decides that it is valid.  Most probate courts in Texas will require you to hire an attorney for this process.  I usually suggest that a person visit with more than one probate attorney so that they get a true assessment....unfortunately, many people will commit an heir to a probate they done need, when a simple affidavit of heirship would have been sufficient.