Before you can quick jump and start using the the TI-99/A4 MiSTer Core, you have to first understand how TI-99 platform is working, otherwise you won’t have any image to try with.

First you have to have valid bios files for TI-99 platform, that you can find on the internet

Then you should have the following files by md5 sums:

ed8ff714542ba850bdec686840a79217  994agrom.bin -> you have to re-name as 994AGROM.BIN
6cc4bc2b6b3b0c33698e6a03759a4cab  994arom.bin -> you have to re-name as 994AROM.BIN
3169cfe66687d5b9ed45a69da5a12817  disk.bin
7adcaf64272248f7a7161cfc02fd5b3f  spchrom.bin

Checkout pyTIrom repository, which repository will make the bios file packaging and rom file conversion to the proper formats that TI-99/A4 MiSTer core can process.

https://github.com/GHPS/pyTIrom

git clone https://github.com/GHPS/pyTIrom.git

Create tiroms.bin

python3 createImage.py -v tiroms.bin
-- Checking input files --
Checking 994AGROM.BIN                   found
Checking 994AROM.BIN                    found

-- Copying input files --

|--------------
|Image Map
|--------------
|  Applying 65536k of padding.
|--------------
|  Copying 994AGROM.BIN                   done (24576k occupied)
|  Filling reserved 32768k.
|  Applying 8192k of padding.
|--------------
|  Filling reserved 8192k.
|  Filling reserved 32768k.
|  Copying 994AROM.BIN                    done (8192k occupied)
|  Applying 16384k of padding.
|--------------

Target ROM tiroms.bin created

Convert game roms

python3 createImage.py -v --Crom=ParsecC.BIN --Grom=ParsecG.BIN Parsec.BIN
-- Checking input files --
Checking 994AGROM.BIN                   found
Checking 994AROM.BIN                    found
Checking ParsecC.BIN                    found
Checking ParsecG.BIN                    found

-- Copying input files --

|--------------
|Image Map
|--------------
|  Copying ParsecC.BIN                    done (8192k occupied)
|  Applying 57344k of padding.
|--------------
|  Copying 994AGROM.BIN                   done (24576k occupied)
|  Copying ParsecG.BIN                    done (24576k occupied)
|  Applying 16384k of padding.
|--------------
|  Filling reserved 8192k.
|  Filling reserved 32768k.
|  Copying 994AROM.BIN                    done (8192k occupied)
|  Applying 16384k of padding.
|--------------

Target ROM Parsec.BIN created

You can find the DE10-Standard, DE1-SoC and Arrow SoCKit MiSTer Releases under the MiSTer platforms:
http://modernhackers.com/mister/