Running heavy programs isn't possible with the standard install of debian because there is no swap configured.

To check the amount of free memory run:
One can create a swap-file into the rootfs and toggle it on / off with swapon swapoff commands. Another option is to create an independent swap-partition. I activated swap followingly:

1. Created a swap-partition to my sd-card (I used Linux-laptop with sd-card reader, but this can be made with fdisk or parted straight in Debian).

2. I had to find out what is the address of my swap partition:
Lists all disks in the system labeled "swap".

3. To activate swap I edited file /etc/swap:
My swap partition was /dev/mmcblk0p1 so i edited line starting with this line, changing it to following:
Note: fstab is very strict on tabs and spaces so check the right formation from a more accurate source!

Result: Right now I'm running Abiword on one workspace and webbrowser on another with virtually no lag.

free -m says: mem used 121 / 123, swap used 41 / 501

Meaning that my 500 mt swap is propably sufficient