Install the software or download a free version of a music creation program online.
Open the program and create a new file by selecting the "File" menu. Add up to 10 new tracks by selecting "Add New Track" from the File menu.
Import the loops you're going to be using into the program. Download free loops online if you don't have any.
Select a basic drum loop and drag it to the sound interface that displays the list of tracks. Place the drum loop on track 1.
Select a bass sample from the loops and drag the sample to track 2. Press play to see if the bass lines up with the drum sample.
Select a string instrument loop such as violin and drag it to track 3. Add in additional instruments on tracks 4 and below according to your preference.
Mix the tracks by selecting the on-board mixer. Mix track 1 to be the highest and any additional instruments should be lower in volume. Add effects such as echo or compression to the rap beat to enhance it.
Listen to the beat and save it to your computer once you are satisfied.