The first number indicates the duration spent in Malaysia at your chosen institution, and the second number indicates the duration spent overseas at a university in the USA.
For example, a 1+3 transfer programme means that you will study your 1st year in Malaysia at your chosen college / university. After that, you will need to apply for a transfer to a university in the USA to finish your remaining 3 years.
It is worth noting that certain course credits taken at your previous institution may not be counted by the receiving university, so it is important to do some research and speak to college counsellors when applying for transfers.