Slightly different levels of formality. Welsh has a number of registers from slang to highly literary, and the register usually taught to beginners on the Welsh Government sponsored schemes tends to follow a middle path.
- Dw i eisiau cymorth - (I want some help) - commonly used in the usual colloquial register.
- Mae eisiau cymorth arna i or Mae arna i eisiau cymorth is slightly more more formal but still commonly used and worth being familiar with.
A different pattern and meaning:
- Rhaid i mi/fi helpu - I [need to/must] help