A key job of the executor is to determine all assets and debts related to the estate.
This is easier said than done, even if the decedent left what appears to be a very comprehensive and well-organized set of documents. One thing that can be very helpful is the decedent's most recent tax return, which will usually provide information about both assets and debts (see Obtaining Past Tax Returns). Even if you aren't actively looking, you will likely uncover new assets and debts for quite some time, (you'll receive various mailings, for example). So don't think you're done on the first pass!
Assets include things such as real estate, stocks, mutual funds, jewelry, furniture, cars, and so forth: anything that's worth money. You should list all significant and relevant assets in the EstateExec Assets tab (see Enter Asset for instructions). If you aren't sure you are aware of all the decedent's assets, see Finding Assets.
In terms of practical advice, it's not worth it to separately list every single small asset. It's perfectly legitimate to list any significantly valuable asset separately, and just lump the rest into something like "home furnishings", for example. If a brokerage account holds several different stocks and mutual funds, you can just list the whole thing as "Merrill Brokerage Account", for example. If you think you need to list >100 assets, you're probably getting too detailed.
See Determining Value for help with asset valuation.
Debts include things such as mortgages, car loans, large outstanding credit card bills, and so forth. See Finding Debts; you should list all debts in the EstateExec Debts tab (see Enter Debt for instructions);
In terms of practical advice, while you must list anything owed at death as an estate debt, it's probably not worth listing every small utility bill and rent payment incurred during estate administration as an "official" EstateExec debt. You can just pay these off as you go, recording the payments in the EstateExec Cashflow tab (see Manage Estate Cash for instructions).
If you are using EstateExec, you will be able to generate a standard Estate Inventory Report once you enter an estate's assets and debts. Perhaps more importantly, you will then find it much easier to manage the estate financials. When you pay off a debt, a corresponding transaction will automatically be entered in the estate account Cashflow tab, and the amount subtracted from the balance. When you sell an asset, a corresponding transaction will automatically be entered in that same estate account, this time adding the proceeds to the balance. When you allocate an asset for distribution, you will be able to see to the total value of all assets allocated for that particular heir. And so on. This is one of the main benefits of using EstateExec, and it will prove invaluable to you throughout the long-term executor process.