The commands are what we use to write to the configuration database. Since your pipe is so low, I used percentage instead (You can work out what 2% of 512K represents) We create a policer, apply the policer using a firewall filter and apply the firewall filter on the interface for the users excessively downloading files. I posted a few links that help you understand how policers work and how the policed bandwidth work. As soon as you login to the router save your existing configuration like this;
#save my-current-config
then you can enter the commands one line at a time or copy all the commands from 1 or 2 then load them like this:
# load set terminal
[Type ^D at a new line to end input]
<Right-click to paste the copied commands> or you can use CTRl + SHIFT + V to paste to copied commands.
then press Ctrl + D, it will say load complete
You can now enter commit. Or you can enter commit confirmed 60 so the filter is applied for 60 minutes and it will rolback in 60 minutes to your original configuration. If you enter commit before 60 minutes it will be applied permanently. You can always load your saved config if you do not like it. But please test it to see if it will work for you. As you indicated that you do not understand the commands, then you should definitely take a few courses like the IJOS, JRE JIR and JSEC
I have two suggestions for you;
1- You can find out the individual IP address and enter then in a prefix-list like this and the apply the firewall filter with the policer like this:
set policy-options prefix-list excess-downloaders 10.10.90.2/32
set policy-options prefix-list excess-downloaders 10.10.90.3/32
set policy-options prefix-list excess-downloaders 10.10.90.4/32
set firewall policer 2mbps if-exceeding bandwidth-percent 2
set firewall policer 2mbps if-exceeding burst-size-limit 1500
set firewall policer 2mbps then discard
set firewall family inet filter limit-download term limt from source-prefix-list excess-downloaders
set firewall family inet filter limit-download term limt then policer 2mbps
set firewall family inet filter limit-download term else-accept then accept
set interfaces ge-0/0/1.90 family inet filter input limit-download
2- Or like this for the whole subnet- I think this is the one you want:
set firewall policer 2mbps if-exceeding bandwidth-percent 2
set firewall policer 2mbps if-exceeding burst-size-limit 1500
set firewall policer 2mbps then discard
set firewall family inet filter limit-download term limt from source-address 10.10.90.0/24
set firewall family inet filter limit-download term limt then policer 2mbps
set firewall family inet filter limit-download term else-accept then accept
set interfaces ge-0/0/1.90 family inet filter input limit-download